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 $105.40   12.499%   $118.5739   $118.57   $118.55   $118.60  
  Purchase #2 $187.35   8.141%   $202.6022   $202.60   $202.60   $202.60  
  Purchase #3 $116.72   6.327%   $124.1049   $124.10   $124.10   $124.10  
  Purchase #4 $161.63   8.844%   $175.9246   $175.92   $175.90   $175.90  
  Purchase #5 $144.44   5.843%   $152.8796   $152.88   $152.90   $152.90  
  Purchase #6 $242.95   13.190%   $274.9951   $275.00   $275.00   $275.00  
  Purchase #7 $132.94   10.183%   $146.4773   $146.48   $146.50   $146.50  
  7 purchase totals = $1,091.43       $1,195.5576   $1,195.55   $1,195.55   $1,195.60