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 $50.92   13.816%   $57.9551   $57.96   $57.95   $58.00  
  Purchase #2 $123.28   7.607%   $132.6579   $132.66   $132.65   $132.70  
  Purchase #3 $142.25   13.208%   $161.0384   $161.04   $161.05   $161.00  
  Purchase #4 $136.79   9.260%   $149.4568   $149.46   $149.45   $149.50  
  Purchase #5 $146.75   10.375%   $161.9753   $161.98   $162.00   $162.00  
  Purchase #6 $248.76   6.112%   $263.9642   $263.96   $263.95   $264.00  
  Purchase #7 $65.53   6.219%   $69.6053   $69.61   $69.60   $69.60  
  7 purchase totals = $914.28       $996.6530   $996.67   $996.65   $996.80