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 $5.44   13.768%   $6.189   $6.19   $6.20   $6.20  
  Purchase #2 $162.81   13.257%   $184.3937   $184.39   $184.40   $184.40  
  Purchase #3 $16.71   9.708%   $18.3322   $18.33   $18.35   $18.30  
  Purchase #4 $79.88   8.629%   $86.7728   $86.77   $86.75   $86.80  
  Purchase #5 $124.48   13.130%   $140.8242   $140.82   $140.80   $140.80  
  Purchase #6 $7.87   9.779%   $8.6396   $8.64   $8.65   $8.60  
  Purchase #7 $76.95   7.721%   $82.8913   $82.89   $82.90   $82.90  
  7 purchase totals = $474.14       $528.0428   $528.03   $528.05   $528.00