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 $53.51   10.148%   $58.9402   $58.94   $58.95   $58.90  
  Purchase #2 $85.34   9.663%   $93.5864   $93.59   $93.60   $93.60  
  Purchase #3 $106.36   12.788%   $119.9613   $119.96   $119.95   $120.00  
  Purchase #4 $207.59   9.639%   $227.5996   $227.60   $227.60   $227.60  
  Purchase #5 $70.46   9.160%   $76.9141   $76.91   $76.90   $76.90  
  Purchase #6 $48.25   4.863%   $50.5964   $50.60   $50.60   $50.60  
  Purchase #7 $180.61   8.446%   $195.8643   $195.86   $195.85   $195.90  
  7 purchase totals = $752.12       $823.4623   $823.46   $823.45   $823.50