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	$101.82	6.789%	$108.7326	$108.73	$108.75	$108.70
Purchase #2	$18.78	8.846%	$20.4413	$20.44	$20.45	$20.40
Purchase #3	$120.41	12.808%	$135.8321	$135.83	$135.85	$135.80
Purchase #4	$114.81	7.226%	$123.1062	$123.11	$123.10	$123.10
Purchase #5	$179.49	11.181%	$199.5588	$199.56	$199.55	$199.60
Purchase #6	$98.30	13.723%	$111.7897	$111.79	$111.80	$111.80
Purchase #7	$222.68	7.241%	$238.8043	$238.80	$238.80	$238.80
7 purchase totals =	$856.29		$938.2650	$938.26	$938.30	$938.20