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	$40.66	4.614%	$42.5361	$42.54	$42.55	$42.50
Purchase #2	$31.96	7.850%	$34.4689	$34.47	$34.45	$34.50
Purchase #3	$162.69	6.772%	$173.7074	$173.71	$173.70	$173.70
Purchase #4	$56.81	13.253%	$64.339	$64.34	$64.35	$64.30
Purchase #5	$230.68	10.362%	$254.5831	$254.58	$254.60	$254.60
Purchase #6	$84.94	5.379%	$89.5089	$89.51	$89.50	$89.50
Purchase #7	$241.26	5.604%	$254.7802	$254.78	$254.80	$254.80
7 purchase totals =	$849.00		$913.9236	$913.93	$913.95	$913.90