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 $52.93   7.584%   $56.9442   $56.94   $56.95   $56.90  
  Purchase #2 $57.73   12.123%   $64.7286   $64.73   $64.75   $64.70  
  Purchase #3 $7.43   11.179%   $8.2606   $8.26   $8.25   $8.30  
  Purchase #4 $163.94   7.568%   $176.347   $176.35   $176.35   $176.30  
  Purchase #5 $92.33   3.154%   $95.2421   $95.24   $95.25   $95.20  
  Purchase #6 $29.47   13.277%   $33.3827   $33.38   $33.40   $33.40  
  Purchase #7 $58.85   5.502%   $62.0879   $62.09   $62.10   $62.10  
  7 purchase totals = $462.68       $496.9931   $496.99   $497.05   $496.90