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 $62.69   12.558%   $70.5626   $70.56   $70.55   $70.60  
  Purchase #2 $87.86   8.357%   $95.2025   $95.20   $95.20   $95.20  
  Purchase #3 $221.69   10.733%   $245.484   $245.48   $245.50   $245.50  
  Purchase #4 $48.54   5.693%   $51.3034   $51.30   $51.30   $51.30  
  Purchase #5 $57.54   4.223%   $59.9699   $59.97   $59.95   $60.00  
  Purchase #6 $237.42   13.135%   $268.6051   $268.61   $268.60   $268.60  
  Purchase #7 $18.88   5.165%   $19.8552   $19.86   $19.85   $19.90  
  7 purchase totals = $734.62       $810.9827   $810.98   $810.95   $811.10