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	$66.61	6.668%	$71.0516	$71.05	$71.05	$71.10
Purchase #2	$18.61	9.718%	$20.4185	$20.42	$20.40	$20.40
Purchase #3	$52.78	4.690%	$55.2554	$55.26	$55.25	$55.30
Purchase #4	$17.48	10.271%	$19.2754	$19.28	$19.30	$19.30
Purchase #5	$238.34	9.169%	$260.1934	$260.19	$260.20	$260.20
Purchase #6	$56.73	4.697%	$59.3946	$59.39	$59.40	$59.40
Purchase #7	$35.91	8.441%	$38.9412	$38.94	$38.95	$38.90
7 purchase totals =	$486.46		$524.5301	$524.53	$524.55	$524.60