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	$69.97	12.423%	$78.6624	$78.66	$78.65	$78.70
Purchase #2	$184.44	3.114%	$190.1835	$190.18	$190.20	$190.20
Purchase #3	$66.66	10.191%	$73.4533	$73.45	$73.45	$73.50
Purchase #4	$154.57	4.483%	$161.4994	$161.50	$161.50	$161.50
Purchase #5	$77.53	7.470%	$83.3215	$83.32	$83.30	$83.30
Purchase #6	$18.75	8.658%	$20.3734	$20.37	$20.35	$20.40
Purchase #7	$88.29	13.345%	$100.0723	$100.07	$100.05	$100.10
7 purchase totals =	$660.21		$707.5658	$707.55	$707.50	$707.70