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 $23.78   8.416%   $25.7813   $25.78   $25.80   $25.80  
  Purchase #2 $105.98   10.710%   $117.3305   $117.33   $117.35   $117.30  
  Purchase #3 $33.32   10.222%   $36.726   $36.73   $36.75   $36.70  
  Purchase #4 $232.37   11.393%   $258.8439   $258.84   $258.85   $258.80  
  Purchase #5 $242.39   6.522%   $258.1987   $258.20   $258.20   $258.20  
  Purchase #6 $14.72   4.598%   $15.3968   $15.40   $15.40   $15.40  
  Purchase #7 $43.37   8.593%   $47.0968   $47.10   $47.10   $47.10  
  7 purchase totals = $695.93       $759.3740   $759.38   $759.45   $759.30