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 $184.91   11.643%   $206.4391   $206.44   $206.45   $206.40  
  Purchase #2 $36.69   6.646%   $39.1284   $39.13   $39.15   $39.10  
  Purchase #3 $69.50   10.116%   $76.5306   $76.53   $76.55   $76.50  
  Purchase #4 $48.66   6.617%   $51.8798   $51.88   $51.90   $51.90  
  Purchase #5 $137.42   9.558%   $150.5546   $150.55   $150.55   $150.60  
  Purchase #6 $83.67   9.786%   $91.8579   $91.86   $91.85   $91.90  
  Purchase #7 $74.87   5.482%   $78.9744   $78.97   $78.95   $79.00  
  7 purchase totals = $635.72       $695.3648   $695.36   $695.40   $695.40