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 $105.55   10.123%   $116.2348   $116.23   $116.25   $116.20  
  Purchase #2 $242.89   4.713%   $254.3374   $254.34   $254.35   $254.30  
  Purchase #3 $14.66   10.349%   $16.1772   $16.18   $16.20   $16.20  
  Purchase #4 $245.64   6.790%   $262.319   $262.32   $262.30   $262.30  
  Purchase #5 $78.42   8.544%   $85.1202   $85.12   $85.10   $85.10  
  Purchase #6 $155.93   9.262%   $170.3722   $170.37   $170.35   $170.40  
  Purchase #7 $11.88   5.202%   $12.498   $12.50   $12.50   $12.50  
  7 purchase totals = $854.97       $917.0588   $917.06   $917.05   $917.00