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 $208.74   6.102%   $221.4773   $221.48   $221.50   $221.50  
  Purchase #2 $249.57   4.689%   $261.2723   $261.27   $261.25   $261.30  
  Purchase #3 $14.36   13.843%   $16.3479   $16.35   $16.35   $16.30  
  Purchase #4 $132.60   13.770%   $150.859   $150.86   $150.85   $150.90  
  Purchase #5 $81.30   4.304%   $84.7992   $84.80   $84.80   $84.80  
  Purchase #6 $154.72   4.822%   $162.1806   $162.18   $162.20   $162.20  
  Purchase #7 $113.55   11.446%   $126.5469   $126.55   $126.55   $126.50  
  7 purchase totals = $954.84       $1,023.4832   $1,023.49   $1,023.50   $1,023.50