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 $108.28   10.326%   $119.461   $119.46   $119.45   $119.50  
  Purchase #2 $218.67   4.702%   $228.9519   $228.95   $228.95   $229.00  
  Purchase #3 $53.43   4.128%   $55.6356   $55.64   $55.65   $55.60  
  Purchase #4 $115.41   5.262%   $121.4829   $121.48   $121.50   $121.50  
  Purchase #5 $242.41   10.197%   $267.1285   $267.13   $267.15   $267.10  
  Purchase #6 $205.90   10.216%   $226.9347   $226.93   $226.95   $226.90  
  Purchase #7 $21.32   4.287%   $22.234   $22.23   $22.25   $22.20  
  7 purchase totals = $965.42       $1,041.8286   $1,041.82   $1,041.90   $1,041.80