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 $14.83   10.153%   $16.3357   $16.34   $16.35   $16.30  
  Purchase #2 $39.77   9.338%   $43.4837   $43.48   $43.50   $43.50  
  Purchase #3 $61.78   11.643%   $68.973   $68.97   $68.95   $69.00  
  Purchase #4 $242.91   9.395%   $265.7314   $265.73   $265.75   $265.70  
  Purchase #5 $191.89   9.451%   $210.0255   $210.03   $210.05   $210.00  
  Purchase #6 $108.94   10.475%   $120.3515   $120.35   $120.35   $120.40  
  Purchase #7 $222.57   8.606%   $241.7244   $241.72   $241.70   $241.70  
  7 purchase totals = $882.69       $966.6252   $966.62   $966.65   $966.60