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	$141.28	12.125%	$158.4102	$158.41	$158.40	$158.40
Purchase #2	$196.26	11.853%	$219.5227	$219.52	$219.50	$219.50
Purchase #3	$80.53	10.652%	$89.1081	$89.11	$89.10	$89.10
Purchase #4	$22.65	6.785%	$24.1868	$24.19	$24.20	$24.20
Purchase #5	$233.80	8.811%	$254.4001	$254.40	$254.40	$254.40
Purchase #6	$79.38	13.487%	$90.086	$90.09	$90.10	$90.10
Purchase #7	$31.25	10.751%	$34.6097	$34.61	$34.60	$34.60
7 purchase totals =	$785.15		$870.3236	$870.33	$870.30	$870.30