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 $90.29   12.151%   $101.2611   $101.26   $101.25   $101.30  
  Purchase #2 $238.80   13.568%   $271.2004   $271.20   $271.20   $271.20  
  Purchase #3 $145.99   5.251%   $153.6559   $153.66   $153.65   $153.70  
  Purchase #4 $76.41   8.109%   $82.6061   $82.61   $82.60   $82.60  
  Purchase #5 $165.45   4.752%   $173.3122   $173.31   $173.30   $173.30  
  Purchase #6 $159.64   9.850%   $175.3645   $175.36   $175.35   $175.40  
  Purchase #7 $248.62   3.525%   $257.3839   $257.38   $257.40   $257.40  
  7 purchase totals = $1,125.20       $1,214.7841   $1,214.78   $1,214.75   $1,214.90