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 $109.73   8.784%   $119.3687   $119.37   $119.35   $119.40  
  Purchase #2 $244.76   11.270%   $272.3445   $272.34   $272.35   $272.30  
  Purchase #3 $24.64   3.325%   $25.4593   $25.46   $25.45   $25.50  
  Purchase #4 $43.85   5.387%   $46.2122   $46.21   $46.20   $46.20  
  Purchase #5 $205.45   4.447%   $214.5864   $214.59   $214.60   $214.60  
  Purchase #6 $56.27   8.298%   $60.9393   $60.94   $60.95   $60.90  
  Purchase #7 $116.61   3.396%   $120.5701   $120.57   $120.55   $120.60  
  7 purchase totals = $801.31       $859.4805   $859.48   $859.45   $859.50