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 $170.86   5.646%   $180.5068   $180.51   $180.50   $180.50  
  Purchase #2 $124.64   13.267%   $141.176   $141.18   $141.20   $141.20  
  Purchase #3 $131.97   12.530%   $148.5058   $148.51   $148.50   $148.50  
  Purchase #4 $122.96   10.652%   $136.0577   $136.06   $136.05   $136.10  
  Purchase #5 $105.64   9.163%   $115.3198   $115.32   $115.30   $115.30  
  Purchase #6 $56.45   8.220%   $61.0902   $61.09   $61.10   $61.10  
  Purchase #7 $119.48   11.625%   $133.3696   $133.37   $133.35   $133.40  
  7 purchase totals = $832.00       $916.0259   $916.04   $916.00   $916.10