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 $202.50   11.227%   $225.2347   $225.23   $225.25   $225.20  
  Purchase #2 $155.63   4.329%   $162.3672   $162.37   $162.35   $162.40  
  Purchase #3 $233.47   12.721%   $263.1697   $263.17   $263.15   $263.20  
  Purchase #4 $231.97   11.335%   $258.2638   $258.26   $258.25   $258.30  
  Purchase #5 $87.74   5.370%   $92.4516   $92.45   $92.45   $92.50  
  Purchase #6 $99.72   13.604%   $113.2859   $113.29   $113.30   $113.30  
  Purchase #7 $165.87   7.766%   $178.7515   $178.75   $178.75   $178.80  
  7 purchase totals = $1,176.90       $1,293.5244   $1,293.52   $1,293.50   $1,293.70