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	$91.30	9.248%	$99.7434	$99.74	$99.75	$99.70
Purchase #2	$147.43	5.814%	$156.0016	$156.00	$156.00	$156.00
Purchase #3	$123.66	12.747%	$139.4229	$139.42	$139.40	$139.40
Purchase #4	$132.74	3.455%	$137.3262	$137.33	$137.35	$137.30
Purchase #5	$82.92	9.853%	$91.0901	$91.09	$91.10	$91.10
Purchase #6	$13.83	11.242%	$15.3848	$15.38	$15.40	$15.40
Purchase #7	$79.66	4.687%	$83.3937	$83.39	$83.40	$83.40
7 purchase totals =	$671.54		$722.3627	$722.35	$722.40	$722.30