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 $186.78   3.828%   $193.9299   $193.93   $193.95   $193.90  
  Purchase #2 $245.89   11.387%   $273.8895   $273.89   $273.90   $273.90  
  Purchase #3 $83.95   13.433%   $95.227   $95.23   $95.25   $95.20  
  Purchase #4 $91.92   13.342%   $104.184   $104.18   $104.20   $104.20  
  Purchase #5 $101.55   10.810%   $112.5276   $112.53   $112.55   $112.50  
  Purchase #6 $8.87   12.618%   $9.9892   $9.99   $10.00   $10.00  
  Purchase #7 $190.44   11.563%   $212.4606   $212.46   $212.45   $212.50  
  7 purchase totals = $909.40       $1,002.2078   $1,002.21   $1,002.30   $1,002.20