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 $54.43   5.713%   $57.5396   $57.54   $57.55   $57.50  
  Purchase #2 $117.48   4.118%   $122.3178   $122.32   $122.30   $122.30  
  Purchase #3 $56.34   11.197%   $62.6484   $62.65   $62.65   $62.60  
  Purchase #4 $14.77   10.285%   $16.2891   $16.29   $16.30   $16.30  
  Purchase #5 $32.77   3.143%   $33.8   $33.80   $33.80   $33.80  
  Purchase #6 $238.85   8.361%   $258.8202   $258.82   $258.80   $258.80  
  Purchase #7 $54.74   6.136%   $58.0988   $58.10   $58.10   $58.10  
  7 purchase totals = $569.38       $609.5139   $609.52   $609.50   $609.40