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	$222.57	12.873%	$251.2214	$251.22	$251.20	$251.20
Purchase #2	$165.84	9.336%	$181.3228	$181.32	$181.30	$181.30
Purchase #3	$184.51	13.680%	$209.751	$209.75	$209.75	$209.80
Purchase #4	$20.90	4.693%	$21.8808	$21.88	$21.90	$21.90
Purchase #5	$40.88	3.392%	$42.2666	$42.27	$42.25	$42.30
Purchase #6	$49.91	13.364%	$56.58	$56.58	$56.60	$56.60
Purchase #7	$179.59	5.784%	$189.9775	$189.98	$190.00	$190.00
7 purchase totals =	$864.20		$953.0001	$953.00	$953.00	$953.10