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	$156.90	10.291%	$173.0466	$173.05	$173.05	$173.00
Purchase #2	$82.86	8.580%	$89.9694	$89.97	$89.95	$90.00
Purchase #3	$51.62	7.696%	$55.5927	$55.59	$55.60	$55.60
Purchase #4	$65.75	9.274%	$71.8477	$71.85	$71.85	$71.80
Purchase #5	$227.70	10.359%	$251.2874	$251.29	$251.30	$251.30
Purchase #6	$194.79	5.580%	$205.6593	$205.66	$205.65	$205.70
Purchase #7	$53.57	10.350%	$59.1145	$59.11	$59.10	$59.10
7 purchase totals =	$833.19		$906.5176	$906.52	$906.50	$906.50