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 $57.61   11.746%   $64.3769   $64.38   $64.40   $64.40  
  Purchase #2 $22.38   11.555%   $24.966   $24.97   $24.95   $25.00  
  Purchase #3 $56.76   10.436%   $62.6835   $62.68   $62.70   $62.70  
  Purchase #4 $48.48   9.720%   $53.1923   $53.19   $53.20   $53.20  
  Purchase #5 $193.61   13.208%   $219.182   $219.18   $219.20   $219.20  
  Purchase #6 $217.32   8.699%   $236.2247   $236.22   $236.20   $236.20  
  Purchase #7 $160.51   9.221%   $175.3106   $175.31   $175.30   $175.30  
  7 purchase totals = $756.67       $835.9360   $835.93   $835.95   $836.00