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 $184.97   7.703%   $199.2182   $199.22   $199.20   $199.20  
  Purchase #2 $190.93   11.358%   $212.6158   $212.62   $212.60   $212.60  
  Purchase #3 $20.61   9.209%   $22.508   $22.51   $22.50   $22.50  
  Purchase #4 $227.62   6.697%   $242.8637   $242.86   $242.85   $242.90  
  Purchase #5 $76.98   13.409%   $87.3022   $87.30   $87.30   $87.30  
  Purchase #6 $173.81   12.569%   $195.6562   $195.66   $195.65   $195.70  
  Purchase #7 $173.86   10.738%   $192.5291   $192.53   $192.55   $192.50  
  7 purchase totals = $1,048.78       $1,152.6932   $1,152.70   $1,152.65   $1,152.70