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	$84.99	4.859%	$89.1197	$89.12	$89.10	$89.10
Purchase #2	$233.86	13.481%	$265.3867	$265.39	$265.40	$265.40
Purchase #3	$132.84	10.856%	$147.2611	$147.26	$147.25	$147.30
Purchase #4	$180.29	5.775%	$190.7017	$190.70	$190.70	$190.70
Purchase #5	$127.51	6.694%	$136.0455	$136.05	$136.05	$136.00
Purchase #6	$52.28	13.426%	$59.2991	$59.30	$59.30	$59.30
Purchase #7	$188.26	6.399%	$200.3068	$200.31	$200.30	$200.30
7 purchase totals =	$1,000.03		$1,088.1206	$1,088.13	$1,088.10	$1,088.10