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	$124.76	13.273%	$141.3194	$141.32	$141.30	$141.30
Purchase #2	$11.71	4.252%	$12.2079	$12.21	$12.20	$12.20
Purchase #3	$94.62	13.407%	$107.3057	$107.31	$107.30	$107.30
Purchase #4	$166.87	7.645%	$179.6272	$179.63	$179.65	$179.60
Purchase #5	$136.88	10.313%	$150.9964	$151.00	$151.00	$151.00
Purchase #6	$64.80	4.327%	$67.6039	$67.60	$67.60	$67.60
Purchase #7	$123.67	3.223%	$127.6559	$127.66	$127.65	$127.70
7 purchase totals =	$723.31		$786.7164	$786.73	$786.70	$786.70