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 $101.86   3.614%   $105.5412   $105.54   $105.55   $105.50  
  Purchase #2 $23.73   8.277%   $25.6941   $25.69   $25.70   $25.70  
  Purchase #3 $91.44   13.596%   $103.8722   $103.87   $103.85   $103.90  
  Purchase #4 $184.59   8.145%   $199.6249   $199.62   $199.60   $199.60  
  Purchase #5 $153.39   5.207%   $161.377   $161.38   $161.40   $161.40  
  Purchase #6 $224.69   11.620%   $250.799   $250.80   $250.80   $250.80  
  Purchase #7 $176.33   3.754%   $182.9494   $182.95   $182.95   $182.90  
  7 purchase totals = $956.03       $1,029.8578   $1,029.85   $1,029.85   $1,029.80