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 $66.68   12.771%   $75.1957   $75.20   $75.20   $75.20  
  Purchase #2 $49.47   8.345%   $53.5983   $53.60   $53.60   $53.60  
  Purchase #3 $140.34   4.387%   $146.4967   $146.50   $146.50   $146.50  
  Purchase #4 $49.73   10.663%   $55.0327   $55.03   $55.05   $55.00  
  Purchase #5 $227.80   10.119%   $250.8511   $250.85   $250.85   $250.90  
  Purchase #6 $152.34   12.673%   $171.646   $171.65   $171.65   $171.60  
  Purchase #7 $32.79   3.801%   $34.0363   $34.04   $34.05   $34.00  
  7 purchase totals = $719.15       $786.8568   $786.87   $786.90   $786.80