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	$36.41	8.179%	$39.388	$39.39	$39.40	$39.40
Purchase #2	$161.26	11.276%	$179.4437	$179.44	$179.45	$179.40
Purchase #3	$229.50	13.505%	$260.494	$260.49	$260.50	$260.50
Purchase #4	$242.47	10.604%	$268.1815	$268.18	$268.20	$268.20
Purchase #5	$82.82	7.488%	$89.0216	$89.02	$89.00	$89.00
Purchase #6	$223.45	6.821%	$238.6915	$238.69	$238.70	$238.70
Purchase #7	$148.59	4.708%	$155.5856	$155.59	$155.60	$155.60
7 purchase totals =	$1,124.50		$1,230.8059	$1,230.80	$1,230.85	$1,230.80