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 $64.39   5.866%   $68.1671   $68.17   $68.15   $68.20  
  Purchase #2 $212.63   13.435%   $241.1968   $241.20   $241.20   $241.20  
  Purchase #3 $101.50   5.678%   $107.2632   $107.26   $107.25   $107.30  
  Purchase #4 $196.37   5.583%   $207.3333   $207.33   $207.35   $207.30  
  Purchase #5 $136.52   5.255%   $143.6941   $143.69   $143.70   $143.70  
  Purchase #6 $24.28   10.129%   $26.7393   $26.74   $26.75   $26.70  
  Purchase #7 $6.61   4.258%   $6.8915   $6.89   $6.90   $6.90  
  7 purchase totals = $742.30       $801.2853   $801.28   $801.30   $801.30