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 $196.47   3.526%   $203.3975   $203.40   $203.40   $203.40  
  Purchase #2 $94.75   7.248%   $101.6175   $101.62   $101.60   $101.60  
  Purchase #3 $227.62   4.571%   $238.0245   $238.02   $238.00   $238.00  
  Purchase #4 $210.73   6.459%   $224.3411   $224.34   $224.35   $224.30  
  Purchase #5 $9.66   13.415%   $10.9559   $10.96   $10.95   $11.00  
  Purchase #6 $31.76   4.567%   $33.2105   $33.21   $33.20   $33.20  
  Purchase #7 $151.36   7.146%   $162.1762   $162.18   $162.20   $162.20  
  7 purchase totals = $922.35       $973.7232   $973.73   $973.70   $973.70