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	$234.96	6.201%	$249.5299	$249.53	$249.55	$249.50
Purchase #2	$205.87	5.111%	$216.392	$216.39	$216.40	$216.40
Purchase #3	$159.72	13.607%	$181.4531	$181.45	$181.45	$181.50
Purchase #4	$65.61	11.599%	$73.2201	$73.22	$73.20	$73.20
Purchase #5	$11.79	6.233%	$12.5249	$12.52	$12.50	$12.50
Purchase #6	$208.65	3.765%	$216.5057	$216.51	$216.50	$216.50
Purchase #7	$19.89	4.360%	$20.7572	$20.76	$20.75	$20.80
7 purchase totals =	$906.49		$970.3829	$970.38	$970.35	$970.40