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 $87.43   7.221%   $93.7433   $93.74   $93.75   $93.70  
  Purchase #2 $207.90   9.316%   $227.268   $227.27   $227.25   $227.30  
  Purchase #3 $49.90   11.822%   $55.7992   $55.80   $55.80   $55.80  
  Purchase #4 $30.66   4.432%   $32.0189   $32.02   $32.00   $32.00  
  Purchase #5 $54.34   5.626%   $57.3972   $57.40   $57.40   $57.40  
  Purchase #6 $194.93   10.737%   $215.8596   $215.86   $215.85   $215.90  
  Purchase #7 $233.37   4.733%   $244.4154   $244.42   $244.40   $244.40  
  7 purchase totals = $858.53       $926.5016   $926.51   $926.45   $926.50