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 $61.96   11.442%   $69.0495   $69.05   $69.05   $69.00  
  Purchase #2 $13.47   11.156%   $14.9727   $14.97   $14.95   $15.00  
  Purchase #3 $164.48   6.808%   $175.6778   $175.68   $175.70   $175.70  
  Purchase #4 $82.89   4.657%   $86.7502   $86.75   $86.75   $86.80  
  Purchase #5 $87.95   9.405%   $96.2217   $96.22   $96.20   $96.20  
  Purchase #6 $151.92   7.191%   $162.8446   $162.84   $162.85   $162.80  
  Purchase #7 $29.67   3.829%   $30.8061   $30.81   $30.80   $30.80  
  7 purchase totals = $592.34       $636.3226   $636.32   $636.30   $636.30