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 $208.48   12.233%   $233.9834   $233.98   $234.00   $234.00  
  Purchase #2 $180.78   10.319%   $199.4347   $199.43   $199.45   $199.40  
  Purchase #3 $196.87   3.477%   $203.7152   $203.72   $203.70   $203.70  
  Purchase #4 $178.77   3.127%   $184.3601   $184.36   $184.35   $184.40  
  Purchase #5 $186.87   8.553%   $202.853   $202.85   $202.85   $202.90  
  Purchase #6 $82.57   3.318%   $85.3097   $85.31   $85.30   $85.30  
  Purchase #7 $216.45   3.587%   $224.2141   $224.21   $224.20   $224.20  
  7 purchase totals = $1,250.79       $1,333.8702   $1,333.86   $1,333.85   $1,333.90