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	$124.98	11.251%	$139.0415	$139.04	$139.05	$139.00
Purchase #2	$238.84	4.282%	$249.0671	$249.07	$249.05	$249.10
Purchase #3	$112.31	12.258%	$126.077	$126.08	$126.10	$126.10
Purchase #4	$107.25	3.658%	$111.1732	$111.17	$111.15	$111.20
Purchase #5	$232.27	3.601%	$240.634	$240.63	$240.65	$240.60
Purchase #6	$246.64	4.717%	$258.274	$258.27	$258.25	$258.30
Purchase #7	$137.89	13.322%	$156.2597	$156.26	$156.25	$156.30
7 purchase totals =	$1,200.18		$1,280.5265	$1,280.52	$1,280.50	$1,280.60