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 $53.39   10.823%   $59.1684   $59.17   $59.15   $59.20  
  Purchase #2 $117.33   13.781%   $133.4992   $133.50   $133.50   $133.50  
  Purchase #3 $20.49   10.490%   $22.6394   $22.64   $22.65   $22.60  
  Purchase #4 $113.94   7.870%   $122.9071   $122.91   $122.90   $122.90  
  Purchase #5 $233.82   6.532%   $249.0931   $249.09   $249.10   $249.10  
  Purchase #6 $169.89   12.408%   $190.97   $190.97   $190.95   $191.00  
  Purchase #7 $159.55   5.261%   $167.9439   $167.94   $167.95   $167.90  
  7 purchase totals = $868.41       $946.2211   $946.22   $946.20   $946.20