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 $236.80   13.141%   $267.9179   $267.92   $267.90   $267.90  
  Purchase #2 $34.54   4.619%   $36.1354   $36.14   $36.15   $36.10  
  Purchase #3 $41.90   10.850%   $46.4462   $46.45   $46.45   $46.40  
  Purchase #4 $200.50   11.756%   $224.0708   $224.07   $224.05   $224.10  
  Purchase #5 $116.88   7.603%   $125.7664   $125.77   $125.75   $125.80  
  Purchase #6 $148.58   6.137%   $157.6984   $157.70   $157.70   $157.70  
  Purchase #7 $140.42   3.520%   $145.3628   $145.36   $145.35   $145.40  
  7 purchase totals = $919.62       $1,003.3979   $1,003.41   $1,003.35   $1,003.40