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 $80.89   12.801%   $91.2447   $91.24   $91.25   $91.20  
  Purchase #2 $160.29   5.182%   $168.5962   $168.60   $168.60   $168.60  
  Purchase #3 $191.89   12.257%   $215.41   $215.41   $215.40   $215.40  
  Purchase #4 $237.96   13.182%   $269.3279   $269.33   $269.35   $269.30  
  Purchase #5 $33.46   4.375%   $34.9239   $34.92   $34.90   $34.90  
  Purchase #6 $101.63   11.164%   $112.976   $112.98   $113.00   $113.00  
  Purchase #7 $5.75   4.488%   $6.0081   $6.01   $6.00   $6.00  
  7 purchase totals = $811.87       $898.4868   $898.49   $898.50   $898.40