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	$83.89	10.341%	$92.5651	$92.57	$92.55	$92.60
Purchase #2	$168.74	8.707%	$183.4322	$183.43	$183.45	$183.40
Purchase #3	$92.29	8.689%	$100.3091	$100.31	$100.30	$100.30
Purchase #4	$128.74	5.585%	$135.9301	$135.93	$135.95	$135.90
Purchase #5	$244.39	7.788%	$263.4231	$263.42	$263.40	$263.40
Purchase #6	$151.25	13.209%	$171.2286	$171.23	$171.25	$171.20
Purchase #7	$122.94	4.618%	$128.6174	$128.62	$128.60	$128.60
7 purchase totals =	$992.24		$1,075.5056	$1,075.51	$1,075.50	$1,075.40