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	$230.37	12.179%	$258.4268	$258.43	$258.45	$258.40
Purchase #2	$178.31	10.451%	$196.9452	$196.95	$196.95	$196.90
Purchase #3	$193.62	10.428%	$213.8107	$213.81	$213.80	$213.80
Purchase #4	$91.79	9.842%	$100.824	$100.82	$100.80	$100.80
Purchase #5	$60.99	13.700%	$69.3456	$69.35	$69.35	$69.30
Purchase #6	$129.92	11.202%	$144.4736	$144.47	$144.45	$144.50
Purchase #7	$104.41	4.222%	$108.8182	$108.82	$108.80	$108.80
7 purchase totals =	$989.41		$1,092.6441	$1,092.65	$1,092.60	$1,092.50