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 $38.27   3.561%   $39.6328   $39.63   $39.65   $39.60  
  Purchase #2 $221.54   11.242%   $246.4455   $246.45   $246.45   $246.40  
  Purchase #3 $211.32   8.630%   $229.5569   $229.56   $229.55   $229.60  
  Purchase #4 $205.78   6.131%   $218.3964   $218.40   $218.40   $218.40  
  Purchase #5 $241.44   11.409%   $268.9859   $268.99   $269.00   $269.00  
  Purchase #6 $146.76   13.827%   $167.0525   $167.05   $167.05   $167.10  
  Purchase #7 $233.76   5.228%   $245.981   $245.98   $246.00   $246.00  
  7 purchase totals = $1,298.87       $1,416.0510   $1,416.06   $1,416.10   $1,416.10