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 $235.34   12.136%   $263.9009   $263.90   $263.90   $263.90  
  Purchase #2 $113.69   4.834%   $119.1858   $119.19   $119.20   $119.20  
  Purchase #3 $250.37   7.689%   $269.6209   $269.62   $269.60   $269.60  
  Purchase #4 $215.89   6.531%   $229.9898   $229.99   $230.00   $230.00  
  Purchase #5 $48.85   8.312%   $52.9104   $52.91   $52.90   $52.90  
  Purchase #6 $226.75   8.755%   $246.602   $246.60   $246.60   $246.60  
  Purchase #7 $169.51   8.447%   $183.8285   $183.83   $183.85   $183.80  
  7 purchase totals = $1,260.40       $1,366.0383   $1,366.04   $1,366.05   $1,366.00