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 $224.64   7.487%   $241.4588   $241.46   $241.45   $241.50  
  Purchase #2 $96.31   12.784%   $108.6223   $108.62   $108.60   $108.60  
  Purchase #3 $209.63   12.572%   $235.9847   $235.98   $236.00   $236.00  
  Purchase #4 $108.78   3.562%   $112.6547   $112.65   $112.65   $112.70  
  Purchase #5 $165.61   11.501%   $184.6568   $184.66   $184.65   $184.70  
  Purchase #6 $45.67   3.794%   $47.4027   $47.40   $47.40   $47.40  
  Purchase #7 $24.52   4.691%   $25.6702   $25.67   $25.65   $25.70  
  7 purchase totals = $875.16       $956.4502   $956.44   $956.40   $956.60