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 $63.85   11.294%   $71.0612   $71.06   $71.05   $71.10  
  Purchase #2 $203.89   11.606%   $227.5535   $227.55   $227.55   $227.60  
  Purchase #3 $70.98   12.519%   $79.866   $79.87   $79.85   $79.90  
  Purchase #4 $11.95   10.716%   $13.2306   $13.23   $13.25   $13.20  
  Purchase #5 $249.90   8.171%   $270.3193   $270.32   $270.30   $270.30  
  Purchase #6 $30.82   12.664%   $34.723   $34.72   $34.70   $34.70  
  Purchase #7 $236.53   8.589%   $256.8456   $256.85   $256.85   $256.80  
  7 purchase totals = $867.92       $953.5992   $953.60   $953.55   $953.60