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 $41.70   12.208%   $46.7907   $46.79   $46.80   $46.80  
  Purchase #2 $171.49   12.604%   $193.1046   $193.10   $193.10   $193.10  
  Purchase #3 $107.55   4.854%   $112.7705   $112.77   $112.75   $112.80  
  Purchase #4 $246.35   12.162%   $276.3111   $276.31   $276.30   $276.30  
  Purchase #5 $232.38   11.775%   $259.7427   $259.74   $259.75   $259.70  
  Purchase #6 $48.39   13.287%   $54.8196   $54.82   $54.80   $54.80  
  Purchase #7 $84.41   12.747%   $95.1697   $95.17   $95.15   $95.20  
  7 purchase totals = $932.27       $1,038.7089   $1,038.70   $1,038.65   $1,038.70