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 $247.65   10.606%   $273.9158   $273.92   $273.90   $273.90  
  Purchase #2 $216.63   8.780%   $235.6501   $235.65   $235.65   $235.70  
  Purchase #3 $54.93   11.729%   $61.3727   $61.37   $61.35   $61.40  
  Purchase #4 $75.81   3.441%   $78.4186   $78.42   $78.40   $78.40  
  Purchase #5 $37.91   9.331%   $41.4474   $41.45   $41.45   $41.40  
  Purchase #6 $120.92   11.118%   $134.3639   $134.36   $134.35   $134.40  
  Purchase #7 $113.50   10.141%   $125.01   $125.01   $125.00   $125.00  
  7 purchase totals = $867.35       $950.1785   $950.18   $950.10   $950.20