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	$80.43	11.844%	$89.9561	$89.96	$89.95	$90.00
Purchase #2	$9.59	8.261%	$10.3822	$10.38	$10.40	$10.40
Purchase #3	$232.62	6.302%	$247.2797	$247.28	$247.30	$247.30
Purchase #4	$70.47	12.179%	$79.0525	$79.05	$79.05	$79.10
Purchase #5	$216.46	3.293%	$223.588	$223.59	$223.60	$223.60
Purchase #6	$47.39	10.790%	$52.5034	$52.50	$52.50	$52.50
Purchase #7	$81.76	12.218%	$91.7494	$91.75	$91.75	$91.70
7 purchase totals =	$738.72		$794.5113	$794.51	$794.55	$794.60