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 $88.69   6.709%   $94.6402   $94.64   $94.65   $94.60  
  Purchase #2 $250.53   3.665%   $259.7119   $259.71   $259.70   $259.70  
  Purchase #3 $133.85   11.567%   $149.3324   $149.33   $149.35   $149.30  
  Purchase #4 $89.73   10.133%   $98.8223   $98.82   $98.80   $98.80  
  Purchase #5 $82.51   9.290%   $90.1752   $90.18   $90.20   $90.20  
  Purchase #6 $196.26   8.161%   $212.2768   $212.28   $212.30   $212.30  
  Purchase #7 $58.81   10.421%   $64.9386   $64.94   $64.95   $64.90  
  7 purchase totals = $900.38       $969.8974   $969.90   $969.95   $969.80