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 $93.95   5.650%   $99.2582   $99.26   $99.25   $99.30  
  Purchase #2 $36.61   8.267%   $39.6365   $39.64   $39.65   $39.60  
  Purchase #3 $216.89   4.816%   $227.3354   $227.34   $227.35   $227.30  
  Purchase #4 $108.28   10.548%   $119.7014   $119.70   $119.70   $119.70  
  Purchase #5 $28.79   11.375%   $32.0649   $32.06   $32.05   $32.10  
  Purchase #6 $220.95   5.444%   $232.9785   $232.98   $233.00   $233.00  
  Purchase #7 $12.34   4.252%   $12.8647   $12.86   $12.85   $12.90  
  7 purchase totals = $717.81       $763.8396   $763.84   $763.85   $763.90