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 $219.59   10.546%   $242.748   $242.75   $242.75   $242.70  
  Purchase #2 $19.57   12.483%   $22.0129   $22.01   $22.00   $22.00  
  Purchase #3 $127.43   3.864%   $132.3539   $132.35   $132.35   $132.40  
  Purchase #4 $170.92   7.378%   $183.5305   $183.53   $183.55   $183.50  
  Purchase #5 $187.50   12.302%   $210.5663   $210.57   $210.55   $210.60  
  Purchase #6 $183.63   12.695%   $206.9418   $206.94   $206.95   $206.90  
  Purchase #7 $242.49   7.832%   $261.4818   $261.48   $261.50   $261.50  
  7 purchase totals = $1,151.13       $1,259.6352   $1,259.63   $1,259.65   $1,259.60