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 $170.44   3.123%   $175.7628   $175.76   $175.75   $175.80  
  Purchase #2 $189.95   12.504%   $213.7013   $213.70   $213.70   $213.70  
  Purchase #3 $69.47   9.731%   $76.2301   $76.23   $76.25   $76.20  
  Purchase #4 $244.97   5.687%   $258.9014   $258.90   $258.90   $258.90  
  Purchase #5 $129.79   3.206%   $133.9511   $133.95   $133.95   $134.00  
  Purchase #6 $119.92   9.737%   $131.5966   $131.60   $131.60   $131.60  
  Purchase #7 $24.87   10.835%   $27.5647   $27.56   $27.55   $27.60  
  7 purchase totals = $949.41       $1,017.7080   $1,017.70   $1,017.70   $1,017.80