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	$75.38	4.134%	$78.4962	$78.50	$78.50	$78.50
Purchase #2	$210.94	5.348%	$222.2211	$222.22	$222.20	$222.20
Purchase #3	$205.58	5.475%	$216.8355	$216.84	$216.85	$216.80
Purchase #4	$174.72	6.224%	$185.5946	$185.59	$185.60	$185.60
Purchase #5	$207.33	7.333%	$222.5335	$222.53	$222.55	$222.50
Purchase #6	$158.29	4.272%	$165.0521	$165.05	$165.05	$165.10
Purchase #7	$245.71	13.501%	$278.8833	$278.88	$278.90	$278.90
7 purchase totals =	$1,277.95		$1,369.6163	$1,369.61	$1,369.65	$1,369.60