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	$17.50	7.554%	$18.822	$18.82	$18.80	$18.80
Purchase #2	$54.82	6.280%	$58.2627	$58.26	$58.25	$58.30
Purchase #3	$169.75	9.393%	$185.6946	$185.69	$185.70	$185.70
Purchase #4	$230.91	3.306%	$238.5439	$238.54	$238.55	$238.50
Purchase #5	$140.66	5.137%	$147.8857	$147.89	$147.90	$147.90
Purchase #6	$101.75	13.849%	$115.8414	$115.84	$115.85	$115.80
Purchase #7	$223.45	13.770%	$254.2191	$254.22	$254.20	$254.20
7 purchase totals =	$938.84		$1,019.2694	$1,019.26	$1,019.25	$1,019.20