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	$145.50	13.484%	$165.1192	$165.12	$165.10	$165.10
Purchase #2	$103.86	5.729%	$109.8101	$109.81	$109.80	$109.80
Purchase #3	$168.50	10.121%	$185.5539	$185.55	$185.55	$185.60
Purchase #4	$42.29	3.146%	$43.6204	$43.62	$43.60	$43.60
Purchase #5	$192.29	3.810%	$199.6162	$199.62	$199.60	$199.60
Purchase #6	$14.44	4.760%	$15.1273	$15.13	$15.15	$15.10
Purchase #7	$183.60	3.332%	$189.7176	$189.72	$189.70	$189.70
7 purchase totals =	$850.48		$908.5647	$908.57	$908.50	$908.50