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	$30.73	9.285%	$33.5833	$33.58	$33.60	$33.60
Purchase #2	$88.66	13.183%	$100.348	$100.35	$100.35	$100.30
Purchase #3	$216.27	11.411%	$240.9486	$240.95	$240.95	$240.90
Purchase #4	$20.78	6.433%	$22.1168	$22.12	$22.10	$22.10
Purchase #5	$190.64	10.106%	$209.9061	$209.91	$209.90	$209.90
Purchase #6	$113.86	11.812%	$127.3091	$127.31	$127.30	$127.30
Purchase #7	$199.61	7.727%	$215.0339	$215.03	$215.05	$215.00
7 purchase totals =	$860.55		$949.2458	$949.25	$949.25	$949.10