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 $214.92   11.225%   $239.0448   $239.04   $239.05   $239.00  
  Purchase #2 $23.53   5.371%   $24.7938   $24.79   $24.80   $24.80  
  Purchase #3 $247.97   11.195%   $275.7302   $275.73   $275.75   $275.70  
  Purchase #4 $221.79   5.787%   $234.625   $234.63   $234.65   $234.60  
  Purchase #5 $71.43   5.147%   $75.1065   $75.11   $75.10   $75.10  
  Purchase #6 $106.40   4.408%   $111.0901   $111.09   $111.10   $111.10  
  Purchase #7 $129.53   3.656%   $134.2656   $134.27   $134.25   $134.30  
  7 purchase totals = $1,015.57       $1,094.6560   $1,094.66   $1,094.70   $1,094.60