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 $83.64   10.743%   $92.6254   $92.63   $92.65   $92.60  
  Purchase #2 $191.87   7.744%   $206.7284   $206.73   $206.75   $206.70  
  Purchase #3 $193.77   13.633%   $220.1867   $220.19   $220.20   $220.20  
  Purchase #4 $23.82   7.774%   $25.6718   $25.67   $25.65   $25.70  
  Purchase #5 $69.79   11.267%   $77.6532   $77.65   $77.65   $77.70  
  Purchase #6 $136.89   10.503%   $151.2676   $151.27   $151.25   $151.30  
  Purchase #7 $158.48   4.624%   $165.8081   $165.81   $165.80   $165.80  
  7 purchase totals = $858.26       $939.9412   $939.95   $939.95   $940.00