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 $87.25   13.105%   $98.6841   $98.68   $98.70   $98.70  
  Purchase #2 $138.76   4.429%   $144.9057   $144.91   $144.90   $144.90  
  Purchase #3 $12.97   12.490%   $14.59   $14.59   $14.60   $14.60  
  Purchase #4 $136.55   8.732%   $148.4735   $148.47   $148.45   $148.50  
  Purchase #5 $215.82   4.608%   $225.765   $225.77   $225.75   $225.80  
  Purchase #6 $208.51   12.149%   $233.8419   $233.84   $233.85   $233.80  
  Purchase #7 $5.31   6.264%   $5.6426   $5.64   $5.65   $5.60  
  7 purchase totals = $805.17       $871.9028   $871.90   $871.90   $871.90