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 $243.57   5.762%   $257.6045   $257.60   $257.60   $257.60  
  Purchase #2 $13.46   9.678%   $14.7627   $14.76   $14.75   $14.80  
  Purchase #3 $174.66   13.146%   $197.6208   $197.62   $197.60   $197.60  
  Purchase #4 $123.78   13.716%   $140.7577   $140.76   $140.75   $140.80  
  Purchase #5 $32.76   10.587%   $36.2283   $36.23   $36.25   $36.20  
  Purchase #6 $179.64   11.578%   $200.4387   $200.44   $200.45   $200.40  
  Purchase #7 $48.96   12.317%   $54.9904   $54.99   $55.00   $55.00  
  7 purchase totals = $816.83       $902.4031   $902.40   $902.40   $902.40