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 $53.71   6.501%   $57.2017   $57.20   $57.20   $57.20  
  Purchase #2 $142.91   11.227%   $158.9545   $158.95   $158.95   $159.00  
  Purchase #3 $43.94   9.541%   $48.1323   $48.13   $48.15   $48.10  
  Purchase #4 $240.69   10.251%   $265.3631   $265.36   $265.35   $265.40  
  Purchase #5 $174.34   3.209%   $179.9346   $179.93   $179.95   $179.90  
  Purchase #6 $161.47   8.168%   $174.6589   $174.66   $174.65   $174.70  
  Purchase #7 $62.27   11.483%   $69.4205   $69.42   $69.40   $69.40  
  7 purchase totals = $879.33       $953.6656   $953.65   $953.65   $953.70