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	$9.54	13.524%	$10.8302	$10.83	$10.85	$10.80
Purchase #2	$89.97	9.210%	$98.2562	$98.26	$98.25	$98.30
Purchase #3	$11.99	7.413%	$12.8788	$12.88	$12.90	$12.90
Purchase #4	$127.42	7.289%	$136.7076	$136.71	$136.70	$136.70
Purchase #5	$170.28	11.804%	$190.3799	$190.38	$190.40	$190.40
Purchase #6	$194.79	12.513%	$219.1641	$219.16	$219.15	$219.20
Purchase #7	$101.86	9.470%	$111.5061	$111.51	$111.50	$111.50
7 purchase totals =	$705.85		$779.7229	$779.73	$779.75	$779.80