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 $121.31   12.864%   $136.9153   $136.92   $136.90   $136.90  
  Purchase #2 $235.60   7.788%   $253.9485   $253.95   $253.95   $253.90  
  Purchase #3 $62.94   12.742%   $70.9598   $70.96   $70.95   $71.00  
  Purchase #4 $156.51   10.844%   $173.4819   $173.48   $173.50   $173.50  
  Purchase #5 $58.81   6.108%   $62.4021   $62.40   $62.40   $62.40  
  Purchase #6 $78.74   4.105%   $81.9723   $81.97   $81.95   $82.00  
  Purchase #7 $214.68   7.539%   $230.8647   $230.86   $230.85   $230.90  
  7 purchase totals = $928.59       $1,010.5446   $1,010.54   $1,010.50   $1,010.60