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	$17.30	13.299%	$19.6007	$19.60	$19.60	$19.60
Purchase #2	$200.35	12.765%	$225.9247	$225.92	$225.90	$225.90
Purchase #3	$37.72	3.645%	$39.0949	$39.09	$39.10	$39.10
Purchase #4	$250.26	3.433%	$258.8514	$258.85	$258.85	$258.90
Purchase #5	$90.26	9.418%	$98.7607	$98.76	$98.75	$98.80
Purchase #6	$38.75	12.552%	$43.6139	$43.61	$43.60	$43.60
Purchase #7	$132.86	13.452%	$150.7323	$150.73	$150.75	$150.70
7 purchase totals =	$767.50		$836.5786	$836.56	$836.55	$836.60