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 $210.87   4.330%   $220.0007   $220.00   $220.00   $220.00  
  Purchase #2 $248.62   11.152%   $276.3461   $276.35   $276.35   $276.30  
  Purchase #3 $26.77   13.156%   $30.2919   $30.29   $30.30   $30.30  
  Purchase #4 $239.99   9.283%   $262.2683   $262.27   $262.25   $262.30  
  Purchase #5 $124.70   3.591%   $129.178   $129.18   $129.20   $129.20  
  Purchase #6 $159.59   5.840%   $168.9101   $168.91   $168.90   $168.90  
  Purchase #7 $250.52   6.340%   $266.403   $266.40   $266.40   $266.40  
  7 purchase totals = $1,261.06       $1,353.3981   $1,353.40   $1,353.40   $1,353.40