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 $233.92   11.692%   $261.2699   $261.27   $261.25   $261.30  
  Purchase #2 $95.82   6.534%   $102.0809   $102.08   $102.10   $102.10  
  Purchase #3 $13.98   8.586%   $15.1803   $15.18   $15.20   $15.20  
  Purchase #4 $118.99   4.113%   $123.8841   $123.88   $123.90   $123.90  
  Purchase #5 $12.43   9.421%   $13.601   $13.60   $13.60   $13.60  
  Purchase #6 $63.80   4.225%   $66.4956   $66.50   $66.50   $66.50  
  Purchase #7 $232.48   5.747%   $245.8406   $245.84   $245.85   $245.80  
  7 purchase totals = $771.42       $828.3524   $828.35   $828.40   $828.40