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 $62.34   9.723%   $68.4013   $68.40   $68.40   $68.40  
  Purchase #2 $109.69   7.369%   $117.7731   $117.77   $117.75   $117.80  
  Purchase #3 $47.53   12.124%   $53.2925   $53.29   $53.30   $53.30  
  Purchase #4 $115.54   5.147%   $121.4868   $121.49   $121.50   $121.50  
  Purchase #5 $239.82   9.801%   $263.3248   $263.32   $263.30   $263.30  
  Purchase #6 $104.32   11.134%   $115.935   $115.94   $115.95   $115.90  
  Purchase #7 $152.29   8.861%   $165.7844   $165.78   $165.80   $165.80  
  7 purchase totals = $831.53       $905.9979   $905.99   $906.00   $906.00