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 $237.85   9.434%   $260.2888   $260.29   $260.30   $260.30  
  Purchase #2 $91.53   11.520%   $102.0743   $102.07   $102.05   $102.10  
  Purchase #3 $61.76   9.290%   $67.4975   $67.50   $67.50   $67.50  
  Purchase #4 $236.92   6.714%   $252.8268   $252.83   $252.85   $252.80  
  Purchase #5 $23.43   13.499%   $26.5928   $26.59   $26.60   $26.60  
  Purchase #6 $213.32   5.733%   $225.5496   $225.55   $225.55   $225.50  
  Purchase #7 $100.34   10.234%   $110.6088   $110.61   $110.60   $110.60  
  7 purchase totals = $965.15       $1,045.4386   $1,045.44   $1,045.45   $1,045.40