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 $56.59   13.477%   $64.2166   $64.22   $64.20   $64.20  
  Purchase #2 $86.38   10.755%   $95.6702   $95.67   $95.65   $95.70  
  Purchase #3 $44.92   6.211%   $47.71   $47.71   $47.70   $47.70  
  Purchase #4 $248.47   7.862%   $268.0047   $268.00   $268.00   $268.00  
  Purchase #5 $84.37   13.662%   $95.8966   $95.90   $95.90   $95.90  
  Purchase #6 $223.84   5.277%   $235.652   $235.65   $235.65   $235.70  
  Purchase #7 $133.95   11.143%   $148.876   $148.88   $148.90   $148.90  
  7 purchase totals = $878.52       $956.0261   $956.03   $956.00   $956.10