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 $174.47   4.430%   $182.199   $182.20   $182.20   $182.20  
  Purchase #2 $148.75   13.655%   $169.0618   $169.06   $169.05   $169.10  
  Purchase #3 $208.46   5.142%   $219.179   $219.18   $219.20   $219.20  
  Purchase #4 $157.76   13.788%   $179.5119   $179.51   $179.50   $179.50  
  Purchase #5 $37.69   8.664%   $40.9555   $40.96   $40.95   $41.00  
  Purchase #6 $245.89   10.514%   $271.7429   $271.74   $271.75   $271.70  
  Purchase #7 $103.44   5.214%   $108.8334   $108.83   $108.85   $108.80  
  7 purchase totals = $1,076.46       $1,171.4835   $1,171.48   $1,171.50   $1,171.50