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 $12.69   10.128%   $13.9752   $13.98   $14.00   $14.00  
  Purchase #2 $151.56   4.716%   $158.7076   $158.71   $158.70   $158.70  
  Purchase #3 $124.90   5.816%   $132.1642   $132.16   $132.15   $132.20  
  Purchase #4 $156.54   8.495%   $169.8381   $169.84   $169.85   $169.80  
  Purchase #5 $198.69   13.584%   $225.68   $225.68   $225.70   $225.70  
  Purchase #6 $214.90   7.554%   $231.1335   $231.13   $231.15   $231.10  
  Purchase #7 $14.70   13.529%   $16.6888   $16.69   $16.70   $16.70  
  7 purchase totals = $873.98       $948.1874   $948.19   $948.25   $948.20