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 $141.62   7.834%   $152.7145   $152.71   $152.70   $152.70  
  Purchase #2 $60.68   8.760%   $65.9956   $66.00   $66.00   $66.00  
  Purchase #3 $170.87   8.811%   $185.9254   $185.93   $185.95   $185.90  
  Purchase #4 $104.62   3.608%   $108.3947   $108.39   $108.40   $108.40  
  Purchase #5 $194.36   12.635%   $218.9174   $218.92   $218.90   $218.90  
  Purchase #6 $43.75   8.318%   $47.3891   $47.39   $47.40   $47.40  
  Purchase #7 $210.82   13.676%   $239.6517   $239.65   $239.65   $239.70  
  7 purchase totals = $926.72       $1,018.9884   $1,018.99   $1,019.00   $1,019.00