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 $151.28   13.871%   $172.264   $172.26   $172.25   $172.30  
  Purchase #2 $249.95   6.312%   $265.7268   $265.73   $265.75   $265.70  
  Purchase #3 $117.94   5.332%   $124.2286   $124.23   $124.25   $124.20  
  Purchase #4 $62.52   10.473%   $69.0677   $69.07   $69.05   $69.10  
  Purchase #5 $250.66   4.561%   $262.0926   $262.09   $262.10   $262.10  
  Purchase #6 $30.98   13.110%   $35.0415   $35.04   $35.05   $35.00  
  Purchase #7 $126.27   5.491%   $133.2035   $133.20   $133.20   $133.20  
  7 purchase totals = $989.60       $1,061.6247   $1,061.62   $1,061.65   $1,061.60