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	$85.27	5.533%	$89.988	$89.99	$90.00	$90.00
Purchase #2	$91.61	13.282%	$103.7776	$103.78	$103.80	$103.80
Purchase #3	$130.41	8.366%	$141.3201	$141.32	$141.30	$141.30
Purchase #4	$10.31	3.279%	$10.6481	$10.65	$10.65	$10.60
Purchase #5	$159.32	7.408%	$171.1224	$171.12	$171.10	$171.10
Purchase #6	$34.68	4.423%	$36.2139	$36.21	$36.20	$36.20
Purchase #7	$225.33	8.249%	$243.9175	$243.92	$243.90	$243.90
7 purchase totals =	$736.93		$796.9876	$796.99	$796.95	$796.90