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 $175.49   11.272%   $195.2712   $195.27   $195.25   $195.30  
  Purchase #2 $107.92   4.768%   $113.0656   $113.07   $113.05   $113.10  
  Purchase #3 $241.68   8.264%   $261.6524   $261.65   $261.65   $261.70  
  Purchase #4 $148.83   8.399%   $161.3302   $161.33   $161.35   $161.30  
  Purchase #5 $167.53   10.203%   $184.6231   $184.62   $184.60   $184.60  
  Purchase #6 $175.63   12.476%   $197.5416   $197.54   $197.55   $197.50  
  Purchase #7 $130.63   8.844%   $142.1829   $142.18   $142.20   $142.20  
  7 purchase totals = $1,147.71       $1,255.6670   $1,255.66   $1,255.65   $1,255.70