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 $84.58   11.317%   $94.1519   $94.15   $94.15   $94.20  
  Purchase #2 $104.67   8.127%   $113.1765   $113.18   $113.20   $113.20  
  Purchase #3 $66.98   8.291%   $72.5333   $72.53   $72.55   $72.50  
  Purchase #4 $232.25   5.593%   $245.2397   $245.24   $245.25   $245.20  
  Purchase #5 $129.62   10.270%   $142.932   $142.93   $142.95   $142.90  
  Purchase #6 $9.29   9.818%   $10.2021   $10.20   $10.20   $10.20  
  Purchase #7 $62.64   5.136%   $65.8572   $65.86   $65.85   $65.90  
  7 purchase totals = $690.03       $744.0927   $744.09   $744.15   $744.10