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 $187.30   11.506%   $208.8507   $208.85   $208.85   $208.90  
  Purchase #2 $115.80   9.389%   $126.6725   $126.67   $126.65   $126.70  
  Purchase #3 $209.34   12.129%   $234.7308   $234.73   $234.75   $234.70  
  Purchase #4 $207.36   11.531%   $231.2707   $231.27   $231.25   $231.30  
  Purchase #5 $79.92   9.637%   $87.6219   $87.62   $87.60   $87.60  
  Purchase #6 $14.26   7.121%   $15.2755   $15.28   $15.30   $15.30  
  Purchase #7 $137.53   5.492%   $145.0831   $145.08   $145.10   $145.10  
  7 purchase totals = $951.51       $1,049.5052   $1,049.50   $1,049.50   $1,049.60