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 $207.48   9.148%   $226.4603   $226.46   $226.45   $226.50  
  Purchase #2 $52.94   13.659%   $60.1711   $60.17   $60.15   $60.20  
  Purchase #3 $130.92   4.866%   $137.2906   $137.29   $137.30   $137.30  
  Purchase #4 $244.77   4.298%   $255.2902   $255.29   $255.30   $255.30  
  Purchase #5 $5.63   9.302%   $6.1537   $6.15   $6.15   $6.20  
  Purchase #6 $195.51   12.735%   $220.4082   $220.41   $220.40   $220.40  
  Purchase #7 $119.56   4.240%   $124.6293   $124.63   $124.65   $124.60  
  7 purchase totals = $956.81       $1,030.4034   $1,030.40   $1,030.40   $1,030.50