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	$244.65	11.630%	$273.1028	$273.10	$273.10	$273.10
Purchase #2	$74.39	10.418%	$82.14	$82.14	$82.15	$82.10
Purchase #3	$238.46	6.142%	$253.1062	$253.11	$253.10	$253.10
Purchase #4	$138.59	9.496%	$151.7505	$151.75	$151.75	$151.80
Purchase #5	$75.72	3.343%	$78.2513	$78.25	$78.25	$78.30
Purchase #6	$227.41	10.114%	$250.4102	$250.41	$250.40	$250.40
Purchase #7	$164.47	13.195%	$186.1718	$186.17	$186.15	$186.20
7 purchase totals =	$1,163.69		$1,274.9328	$1,274.93	$1,274.90	$1,275.00