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 $59.67   3.612%   $61.8253   $61.83   $61.85   $61.80  
  Purchase #2 $76.58   12.440%   $86.1066   $86.11   $86.10   $86.10  
  Purchase #3 $179.77   3.267%   $185.6431   $185.64   $185.65   $185.60  
  Purchase #4 $223.59   8.252%   $242.0406   $242.04   $242.05   $242.00  
  Purchase #5 $70.74   8.412%   $76.6906   $76.69   $76.70   $76.70  
  Purchase #6 $153.54   11.259%   $170.8271   $170.83   $170.85   $170.80  
  Purchase #7 $8.83   9.771%   $9.6928   $9.69   $9.70   $9.70  
  7 purchase totals = $772.72       $832.8261   $832.83   $832.90   $832.70