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	$125.57	13.471%	$142.4855	$142.49	$142.50	$142.50
Purchase #2	$226.95	4.202%	$236.4864	$236.49	$236.50	$236.50
Purchase #3	$25.27	7.162%	$27.0798	$27.08	$27.10	$27.10
Purchase #4	$159.54	3.745%	$165.5148	$165.51	$165.50	$165.50
Purchase #5	$134.97	6.484%	$143.7215	$143.72	$143.70	$143.70
Purchase #6	$122.53	3.719%	$127.0869	$127.09	$127.10	$127.10
Purchase #7	$181.90	9.735%	$199.608	$199.61	$199.60	$199.60
7 purchase totals =	$976.73		$1,041.9829	$1,041.99	$1,042.00	$1,042.00