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 $23.46   9.495%   $25.6875   $25.69   $25.70   $25.70  
  Purchase #2 $136.73   10.842%   $151.5543   $151.55   $151.55   $151.60  
  Purchase #3 $227.87   3.251%   $235.2781   $235.28   $235.30   $235.30  
  Purchase #4 $91.88   6.591%   $97.9358   $97.94   $97.95   $97.90  
  Purchase #5 $125.65   4.723%   $131.5844   $131.58   $131.60   $131.60  
  Purchase #6 $151.38   13.778%   $172.2371   $172.24   $172.25   $172.20  
  Purchase #7 $126.30   12.705%   $142.3464   $142.35   $142.35   $142.30  
  7 purchase totals = $883.27       $956.6236   $956.63   $956.70   $956.60