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 $50.86   6.574%   $54.2035   $54.20   $54.20   $54.20  
  Purchase #2 $91.34   3.798%   $94.8091   $94.81   $94.80   $94.80  
  Purchase #3 $17.45   13.192%   $19.752   $19.75   $19.75   $19.80  
  Purchase #4 $43.59   6.734%   $46.5254   $46.53   $46.55   $46.50  
  Purchase #5 $42.83   9.584%   $46.9348   $46.93   $46.95   $46.90  
  Purchase #6 $239.42   7.848%   $258.2097   $258.21   $258.20   $258.20  
  Purchase #7 $220.98   8.354%   $239.4407   $239.44   $239.45   $239.40  
  7 purchase totals = $706.47       $759.8752   $759.87   $759.90   $759.80