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 $240.65   8.577%   $261.2906   $261.29   $261.30   $261.30  
  Purchase #2 $151.39   7.437%   $162.6489   $162.65   $162.65   $162.60  
  Purchase #3 $12.54   10.293%   $13.8307   $13.83   $13.85   $13.80  
  Purchase #4 $205.98   5.303%   $216.9031   $216.90   $216.90   $216.90  
  Purchase #5 $66.81   13.393%   $75.7579   $75.76   $75.75   $75.80  
  Purchase #6 $192.92   11.734%   $215.5572   $215.56   $215.55   $215.60  
  Purchase #7 $38.91   11.471%   $43.3734   $43.37   $43.35   $43.40  
  7 purchase totals = $909.20       $989.3618   $989.36   $989.35   $989.40