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 $95.77   8.643%   $104.0474   $104.05   $104.05   $104.00  
  Purchase #2 $53.92   7.458%   $57.9414   $57.94   $57.95   $57.90  
  Purchase #3 $120.43   9.681%   $132.0888   $132.09   $132.10   $132.10  
  Purchase #4 $70.98   7.571%   $76.3539   $76.35   $76.35   $76.40  
  Purchase #5 $167.36   9.419%   $183.1236   $183.12   $183.10   $183.10  
  Purchase #6 $32.87   5.520%   $34.6844   $34.68   $34.70   $34.70  
  Purchase #7 $170.33   3.394%   $176.111   $176.11   $176.10   $176.10  
  7 purchase totals = $711.66       $764.3505   $764.34   $764.35   $764.30