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 $133.31   13.467%   $151.2629   $151.26   $151.25   $151.30  
  Purchase #2 $191.26   9.725%   $209.86   $209.86   $209.85   $209.90  
  Purchase #3 $45.85   6.465%   $48.8142   $48.81   $48.80   $48.80  
  Purchase #4 $148.98   3.545%   $154.2613   $154.26   $154.25   $154.30  
  Purchase #5 $221.88   10.693%   $245.6056   $245.61   $245.60   $245.60  
  Purchase #6 $41.35   13.602%   $46.9744   $46.97   $46.95   $47.00  
  Purchase #7 $133.37   6.162%   $141.5883   $141.59   $141.60   $141.60  
  7 purchase totals = $916.00       $998.3667   $998.36   $998.30   $998.50