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 $44.38   7.262%   $47.6029   $47.60   $47.60   $47.60  
  Purchase #2 $155.94   12.267%   $175.0692   $175.07   $175.05   $175.10  
  Purchase #3 $220.49   11.265%   $245.3282   $245.33   $245.35   $245.30  
  Purchase #4 $101.96   6.431%   $108.517   $108.52   $108.50   $108.50  
  Purchase #5 $108.70   12.812%   $122.6266   $122.63   $122.65   $122.60  
  Purchase #6 $214.29   4.167%   $223.2195   $223.22   $223.20   $223.20  
  Purchase #7 $65.25   6.302%   $69.3621   $69.36   $69.35   $69.40  
  7 purchase totals = $911.01       $991.7255   $991.73   $991.70   $991.70