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 $108.92   9.831%   $119.6279   $119.63   $119.65   $119.60  
  Purchase #2 $226.97   13.614%   $257.8697   $257.87   $257.85   $257.90  
  Purchase #3 $213.82   13.491%   $242.6665   $242.67   $242.65   $242.70  
  Purchase #4 $164.70   11.614%   $183.8283   $183.83   $183.85   $183.80  
  Purchase #5 $53.78   13.508%   $61.0446   $61.04   $61.05   $61.00  
  Purchase #6 $94.72   12.145%   $106.2237   $106.22   $106.20   $106.20  
  Purchase #7 $12.70   4.106%   $13.2215   $13.22   $13.20   $13.20  
  7 purchase totals = $875.61       $984.4822   $984.48   $984.45   $984.40