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	$170.26	10.569%	$188.2548	$188.25	$188.25	$188.30
Purchase #2	$80.85	6.778%	$86.33	$86.33	$86.35	$86.30
Purchase #3	$233.31	6.834%	$249.2544	$249.25	$249.25	$249.30
Purchase #4	$145.31	7.297%	$155.9133	$155.91	$155.90	$155.90
Purchase #5	$226.61	13.796%	$257.8731	$257.87	$257.85	$257.90
Purchase #6	$19.80	13.252%	$22.4239	$22.42	$22.40	$22.40
Purchase #7	$40.30	4.621%	$42.1623	$42.16	$42.15	$42.20
7 purchase totals =	$916.44		$1,002.2118	$1,002.19	$1,002.15	$1,002.30