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	$158.53	7.393%	$170.2501	$170.25	$170.25	$170.30
Purchase #2	$210.97	10.591%	$233.3138	$233.31	$233.30	$233.30
Purchase #3	$15.48	4.333%	$16.1507	$16.15	$16.15	$16.20
Purchase #4	$78.61	12.548%	$88.474	$88.47	$88.45	$88.50
Purchase #5	$148.42	6.468%	$158.0198	$158.02	$158.00	$158.00
Purchase #6	$52.25	10.416%	$57.6924	$57.69	$57.70	$57.70
Purchase #7	$50.56	13.723%	$57.4983	$57.50	$57.50	$57.50
7 purchase totals =	$714.82		$781.3991	$781.39	$781.35	$781.50