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 $237.28   13.657%   $269.6853   $269.69   $269.70   $269.70  
  Purchase #2 $153.59   11.304%   $170.9518   $170.95   $170.95   $171.00  
  Purchase #3 $58.75   3.372%   $60.7311   $60.73   $60.75   $60.70  
  Purchase #4 $61.89   3.130%   $63.8272   $63.83   $63.85   $63.80  
  Purchase #5 $249.49   6.659%   $266.1035   $266.10   $266.10   $266.10  
  Purchase #6 $149.50   13.519%   $169.7109   $169.71   $169.70   $169.70  
  Purchase #7 $149.45   5.187%   $157.202   $157.20   $157.20   $157.20  
  7 purchase totals = $1,059.95       $1,158.2118   $1,158.21   $1,158.25   $1,158.20