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 $210.86   13.684%   $239.7141   $239.71   $239.70   $239.70  
  Purchase #2 $195.33   11.787%   $218.3535   $218.35   $218.35   $218.40  
  Purchase #3 $206.45   10.202%   $227.512   $227.51   $227.50   $227.50  
  Purchase #4 $31.41   11.644%   $35.0674   $35.07   $35.05   $35.10  
  Purchase #5 $219.96   10.170%   $242.3299   $242.33   $242.35   $242.30  
  Purchase #6 $154.70   3.267%   $159.754   $159.75   $159.75   $159.80  
  Purchase #7 $195.38   3.481%   $202.1812   $202.18   $202.20   $202.20  
  7 purchase totals = $1,214.09       $1,324.9121   $1,324.90   $1,324.90   $1,325.00