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 $96.91   4.222%   $101.0015   $101.00   $101.00   $101.00  
  Purchase #2 $126.43   5.198%   $133.0018   $133.00   $133.00   $133.00  
  Purchase #3 $18.36   9.819%   $20.1628   $20.16   $20.15   $20.20  
  Purchase #4 $208.75   13.650%   $237.2444   $237.24   $237.25   $237.20  
  Purchase #5 $146.66   6.523%   $156.2266   $156.23   $156.25   $156.20  
  Purchase #6 $239.98   12.204%   $269.2672   $269.27   $269.25   $269.30  
  Purchase #7 $244.91   3.674%   $253.908   $253.91   $253.90   $253.90  
  7 purchase totals = $1,082.00       $1,170.8123   $1,170.81   $1,170.80   $1,170.80