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 $58.68   12.447%   $65.9839   $65.98   $66.00   $66.00  
  Purchase #2 $178.39   13.499%   $202.4709   $202.47   $202.45   $202.50  
  Purchase #3 $97.98   13.535%   $111.2416   $111.24   $111.25   $111.20  
  Purchase #4 $55.35   5.402%   $58.34   $58.34   $58.35   $58.30  
  Purchase #5 $150.59   7.168%   $161.3843   $161.38   $161.40   $161.40  
  Purchase #6 $119.93   5.331%   $126.3235   $126.32   $126.30   $126.30  
  Purchase #7 $162.33   5.294%   $170.9238   $170.92   $170.90   $170.90  
  7 purchase totals = $823.25       $896.6680   $896.65   $896.65   $896.60