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	$77.42	11.401%	$86.2467	$86.25	$86.25	$86.20
Purchase #2	$116.55	3.294%	$120.3892	$120.39	$120.40	$120.40
Purchase #3	$92.26	13.286%	$104.5177	$104.52	$104.50	$104.50
Purchase #4	$242.95	5.829%	$257.1116	$257.11	$257.10	$257.10
Purchase #5	$27.61	11.274%	$30.7228	$30.72	$30.70	$30.70
Purchase #6	$82.85	9.718%	$90.9014	$90.90	$90.90	$90.90
Purchase #7	$99.62	3.854%	$103.4594	$103.46	$103.45	$103.50
7 purchase totals =	$739.26		$793.3488	$793.35	$793.30	$793.30