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 $7.61   11.260%   $8.4669   $8.47   $8.45   $8.50  
  Purchase #2 $118.85   10.644%   $131.5004   $131.50   $131.50   $131.50  
  Purchase #3 $50.40   6.708%   $53.7808   $53.78   $53.80   $53.80  
  Purchase #4 $25.97   11.683%   $29.0041   $29.00   $29.00   $29.00  
  Purchase #5 $57.69   7.638%   $62.0964   $62.10   $62.10   $62.10  
  Purchase #6 $93.37   13.748%   $106.2065   $106.21   $106.20   $106.20  
  Purchase #7 $250.34   9.203%   $273.3788   $273.38   $273.40   $273.40  
  7 purchase totals = $604.23       $664.4339   $664.44   $664.45   $664.50