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 $83.51   9.131%   $91.1353   $91.14   $91.15   $91.10  
  Purchase #2 $224.60   12.341%   $252.3179   $252.32   $252.30   $252.30  
  Purchase #3 $180.82   10.205%   $199.2727   $199.27   $199.25   $199.30  
  Purchase #4 $9.67   12.581%   $10.8866   $10.89   $10.90   $10.90  
  Purchase #5 $188.64   4.798%   $197.6909   $197.69   $197.70   $197.70  
  Purchase #6 $113.66   9.527%   $124.4884   $124.49   $124.50   $124.50  
  Purchase #7 $175.35   11.392%   $195.3259   $195.33   $195.35   $195.30  
  7 purchase totals = $976.25       $1,071.1177   $1,071.13   $1,071.15   $1,071.10