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 $98.38   4.636%   $102.9409   $102.94   $102.95   $102.90  
  Purchase #2 $188.33   4.237%   $196.3095   $196.31   $196.30   $196.30  
  Purchase #3 $230.99   6.289%   $245.517   $245.52   $245.50   $245.50  
  Purchase #4 $195.99   6.373%   $208.4804   $208.48   $208.50   $208.50  
  Purchase #5 $125.71   8.219%   $136.0421   $136.04   $136.05   $136.00  
  Purchase #6 $234.74   13.384%   $266.1576   $266.16   $266.15   $266.20  
  Purchase #7 $218.60   12.213%   $245.2976   $245.30   $245.30   $245.30  
  7 purchase totals = $1,292.74       $1,400.7451   $1,400.75   $1,400.75   $1,400.70