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 $247.39   5.746%   $261.605   $261.61   $261.60   $261.60  
  Purchase #2 $48.55   11.676%   $54.2187   $54.22   $54.20   $54.20  
  Purchase #3 $152.54   9.543%   $167.0969   $167.10   $167.10   $167.10  
  Purchase #4 $96.40   8.664%   $104.7521   $104.75   $104.75   $104.80  
  Purchase #5 $226.59   4.717%   $237.2783   $237.28   $237.30   $237.30  
  Purchase #6 $9.70   12.848%   $10.9463   $10.95   $10.95   $10.90  
  Purchase #7 $170.50   4.715%   $178.5391   $178.54   $178.55   $178.50  
  7 purchase totals = $951.67       $1,014.4364   $1,014.45   $1,014.45   $1,014.40