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 $60.44   11.253%   $67.2413   $67.24   $67.25   $67.20  
  Purchase #2 $148.55   10.595%   $164.2889   $164.29   $164.30   $164.30  
  Purchase #3 $150.64   7.257%   $161.5719   $161.57   $161.55   $161.60  
  Purchase #4 $89.61   12.602%   $100.9027   $100.90   $100.90   $100.90  
  Purchase #5 $161.25   8.547%   $175.032   $175.03   $175.05   $175.00  
  Purchase #6 $38.48   5.782%   $40.7049   $40.70   $40.70   $40.70  
  Purchase #7 $170.63   7.731%   $183.8214   $183.82   $183.80   $183.80  
  7 purchase totals = $819.60       $893.5631   $893.55   $893.55   $893.50