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 $112.67   9.813%   $123.7263   $123.73   $123.75   $123.70  
  Purchase #2 $62.40   5.343%   $65.734   $65.73   $65.75   $65.70  
  Purchase #3 $44.39   9.716%   $48.7029   $48.70   $48.70   $48.70  
  Purchase #4 $185.70   8.535%   $201.5495   $201.55   $201.55   $201.50  
  Purchase #5 $111.87   12.413%   $125.7564   $125.76   $125.75   $125.80  
  Purchase #6 $215.92   9.314%   $236.0308   $236.03   $236.05   $236.00  
  Purchase #7 $78.40   6.242%   $83.2937   $83.29   $83.30   $83.30  
  7 purchase totals = $811.35       $884.7936   $884.79   $884.85   $884.70