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 $41.65   6.518%   $44.3647   $44.36   $44.35   $44.40  
  Purchase #2 $109.69   6.423%   $116.7354   $116.74   $116.75   $116.70  
  Purchase #3 $163.60   12.854%   $184.6291   $184.63   $184.65   $184.60  
  Purchase #4 $43.64   10.825%   $48.364   $48.36   $48.35   $48.40  
  Purchase #5 $204.62   5.218%   $215.2971   $215.30   $215.30   $215.30  
  Purchase #6 $175.94   13.325%   $199.384   $199.38   $199.40   $199.40  
  Purchase #7 $141.88   10.536%   $156.8285   $156.83   $156.85   $156.80  
  7 purchase totals = $881.02       $965.6028   $965.60   $965.65   $965.60