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 $227.93   11.134%   $253.3077   $253.31   $253.30   $253.30  
  Purchase #2 $156.42   6.865%   $167.1582   $167.16   $167.15   $167.20  
  Purchase #3 $173.36   10.169%   $190.989   $190.99   $191.00   $191.00  
  Purchase #4 $238.33   6.709%   $254.3196   $254.32   $254.30   $254.30  
  Purchase #5 $32.98   8.804%   $35.8836   $35.88   $35.90   $35.90  
  Purchase #6 $47.34   3.500%   $48.9969   $49.00   $49.00   $49.00  
  Purchase #7 $60.77   3.548%   $62.9261   $62.93   $62.95   $62.90  
  7 purchase totals = $937.13       $1,013.5811   $1,013.59   $1,013.60   $1,013.60