Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $206.77   8.397%   $224.1325   $224.13   $224.15   $224.10  
  Purchase #2 $174.66   7.327%   $187.4573   $187.46   $187.45   $187.50  
  Purchase #3 $181.59   8.294%   $196.6511   $196.65   $196.65   $196.70  
  Purchase #4 $181.98   11.731%   $203.3281   $203.33   $203.35   $203.30  
  Purchase #5 $235.49   4.152%   $245.2675   $245.27   $245.25   $245.30  
  Purchase #6 $244.66   11.849%   $273.6498   $273.65   $273.65   $273.60  
  Purchase #7 $143.65   12.206%   $161.1839   $161.18   $161.20   $161.20  
  7 purchase totals = $1,368.80       $1,491.6702   $1,491.67   $1,491.70   $1,491.70