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 $169.94   13.708%   $193.2354   $193.24   $193.25   $193.20  
  Purchase #2 $54.71   11.365%   $60.9278   $60.93   $60.95   $60.90  
  Purchase #3 $182.33   7.424%   $195.8662   $195.87   $195.85   $195.90  
  Purchase #4 $73.44   12.873%   $82.8939   $82.89   $82.90   $82.90  
  Purchase #5 $182.98   13.330%   $207.3712   $207.37   $207.35   $207.40  
  Purchase #6 $119.35   4.413%   $124.6169   $124.62   $124.60   $124.60  
  Purchase #7 $21.95   10.523%   $24.2598   $24.26   $24.25   $24.30  
  7 purchase totals = $804.70       $889.1712   $889.18   $889.15   $889.20