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 $201.43   6.486%   $214.4947   $214.49   $214.50   $214.50  
  Purchase #2 $168.50   6.463%   $179.3902   $179.39   $179.40   $179.40  
  Purchase #3 $11.97   6.155%   $12.7068   $12.71   $12.70   $12.70  
  Purchase #4 $108.78   6.786%   $116.1618   $116.16   $116.15   $116.20  
  Purchase #5 $22.38   10.655%   $24.7646   $24.76   $24.75   $24.80  
  Purchase #6 $45.94   4.603%   $48.0546   $48.05   $48.05   $48.10  
  Purchase #7 $54.80   9.538%   $60.0268   $60.03   $60.05   $60.00  
  7 purchase totals = $613.80       $655.5995   $655.59   $655.60   $655.70