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 $201.99   10.662%   $223.5262   $223.53   $223.55   $223.50  
  Purchase #2 $48.72   5.399%   $51.3504   $51.35   $51.35   $51.40  
  Purchase #3 $27.85   7.636%   $29.9766   $29.98   $30.00   $30.00  
  Purchase #4 $240.92   7.587%   $259.1986   $259.20   $259.20   $259.20  
  Purchase #5 $83.55   13.224%   $94.5987   $94.60   $94.60   $94.60  
  Purchase #6 $146.99   5.157%   $154.5703   $154.57   $154.55   $154.60  
  Purchase #7 $7.74   12.529%   $8.7097   $8.71   $8.70   $8.70  
  7 purchase totals = $757.76       $821.9305   $821.94   $821.95   $822.00