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 $75.90   3.126%   $78.2726   $78.27   $78.25   $78.30  
  Purchase #2 $242.58   10.501%   $268.0533   $268.05   $268.05   $268.10  
  Purchase #3 $41.62   12.312%   $46.7443   $46.74   $46.75   $46.70  
  Purchase #4 $233.75   5.118%   $245.7133   $245.71   $245.70   $245.70  
  Purchase #5 $67.49   11.686%   $75.3769   $75.38   $75.40   $75.40  
  Purchase #6 $61.69   8.239%   $66.7726   $66.77   $66.75   $66.80  
  Purchase #7 $206.76   13.111%   $233.8683   $233.87   $233.85   $233.90  
  7 purchase totals = $929.79       $1,014.8013   $1,014.79   $1,014.75   $1,014.90