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 $246.74   13.155%   $279.1986   $279.20   $279.20   $279.20  
  Purchase #2 $243.58   8.803%   $265.0223   $265.02   $265.00   $265.00  
  Purchase #3 $59.42   12.743%   $66.9919   $66.99   $67.00   $67.00  
  Purchase #4 $176.91   11.634%   $197.4917   $197.49   $197.50   $197.50  
  Purchase #5 $117.29   13.354%   $132.9529   $132.95   $132.95   $133.00  
  Purchase #6 $49.54   9.674%   $54.3325   $54.33   $54.35   $54.30  
  Purchase #7 $155.77   6.504%   $165.9013   $165.90   $165.90   $165.90  
  7 purchase totals = $1,049.25       $1,161.8912   $1,161.88   $1,161.90   $1,161.90