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 $117.33   8.257%   $127.0179   $127.02   $127.00   $127.00  
  Purchase #2 $190.81   6.807%   $203.7984   $203.80   $203.80   $203.80  
  Purchase #3 $206.68   4.607%   $216.2017   $216.20   $216.20   $216.20  
  Purchase #4 $111.28   12.628%   $125.3324   $125.33   $125.35   $125.30  
  Purchase #5 $127.67   11.120%   $141.8669   $141.87   $141.85   $141.90  
  Purchase #6 $94.37   5.700%   $99.7491   $99.75   $99.75   $99.70  
  Purchase #7 $142.62   9.227%   $155.7795   $155.78   $155.80   $155.80  
  7 purchase totals = $990.76       $1,069.7459   $1,069.75   $1,069.75   $1,069.70