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 $61.44   6.791%   $65.6124   $65.61   $65.60   $65.60  
  Purchase #2 $69.57   5.827%   $73.6238   $73.62   $73.60   $73.60  
  Purchase #3 $126.68   8.270%   $137.1564   $137.16   $137.15   $137.20  
  Purchase #4 $40.63   12.581%   $45.7417   $45.74   $45.75   $45.70  
  Purchase #5 $69.90   4.708%   $73.1909   $73.19   $73.20   $73.20  
  Purchase #6 $32.42   6.260%   $34.4495   $34.45   $34.45   $34.40  
  Purchase #7 $233.60   9.170%   $255.0211   $255.02   $255.00   $255.00  
  7 purchase totals = $634.24       $684.7958   $684.79   $684.75   $684.70