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	$38.29	11.332%	$42.629	$42.63	$42.65	$42.60
Purchase #2	$153.61	12.826%	$173.312	$173.31	$173.30	$173.30
Purchase #3	$80.90	5.624%	$85.4498	$85.45	$85.45	$85.40
Purchase #4	$149.46	5.659%	$157.9179	$157.92	$157.90	$157.90
Purchase #5	$64.37	12.422%	$72.366	$72.37	$72.35	$72.40
Purchase #6	$219.64	8.513%	$238.338	$238.34	$238.35	$238.30
Purchase #7	$187.85	5.419%	$198.0296	$198.03	$198.05	$198.00
7 purchase totals =	$894.12		$968.0423	$968.05	$968.05	$967.90