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 $54.98   12.812%   $62.024   $62.02   $62.00   $62.00  
  Purchase #2 $14.30   8.318%   $15.4895   $15.49   $15.50   $15.50  
  Purchase #3 $13.93   7.683%   $15.0002   $15.00   $15.00   $15.00  
  Purchase #4 $81.36   6.838%   $86.9234   $86.92   $86.90   $86.90  
  Purchase #5 $240.79   5.150%   $253.1907   $253.19   $253.20   $253.20  
  Purchase #6 $79.28   10.727%   $87.7844   $87.78   $87.80   $87.80  
  Purchase #7 $199.83   9.680%   $219.1735   $219.17   $219.15   $219.20  
  7 purchase totals = $684.47       $739.5857   $739.57   $739.55   $739.60