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	$80.72	10.601%	$89.2771	$89.28	$89.30	$89.30
Purchase #2	$70.91	3.273%	$73.2309	$73.23	$73.25	$73.20
Purchase #3	$18.53	9.643%	$20.3168	$20.32	$20.30	$20.30
Purchase #4	$185.25	7.274%	$198.7251	$198.73	$198.75	$198.70
Purchase #5	$196.76	10.831%	$218.0711	$218.07	$218.05	$218.10
Purchase #6	$11.60	6.286%	$12.3292	$12.33	$12.35	$12.30
Purchase #7	$177.41	4.518%	$185.4254	$185.43	$185.45	$185.40
7 purchase totals =	$741.18		$797.3756	$797.39	$797.45	$797.30