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 $13.77   3.140%   $14.2024   $14.20   $14.20   $14.20  
  Purchase #2 $153.85   13.505%   $174.6274   $174.63   $174.65   $174.60  
  Purchase #3 $12.39   13.453%   $14.0568   $14.06   $14.05   $14.10  
  Purchase #4 $113.96   11.337%   $126.8796   $126.88   $126.90   $126.90  
  Purchase #5 $239.77   8.860%   $261.0136   $261.01   $261.00   $261.00  
  Purchase #6 $137.78   6.130%   $146.2259   $146.23   $146.25   $146.20  
  Purchase #7 $147.35   10.158%   $162.3178   $162.32   $162.30   $162.30  
  7 purchase totals = $818.87       $899.3235   $899.33   $899.35   $899.30