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	$141.46	12.338%	$158.9133	$158.91	$158.90	$158.90
Purchase #2	$224.77	8.483%	$243.8372	$243.84	$243.85	$243.80
Purchase #3	$244.63	13.214%	$276.9554	$276.96	$276.95	$277.00
Purchase #4	$78.96	9.140%	$86.1769	$86.18	$86.20	$86.20
Purchase #5	$126.33	3.360%	$130.5747	$130.57	$130.55	$130.60
Purchase #6	$114.49	11.437%	$127.5842	$127.58	$127.60	$127.60
Purchase #7	$88.65	12.571%	$99.7942	$99.79	$99.80	$99.80
7 purchase totals =	$1,019.29		$1,123.8359	$1,123.83	$1,123.85	$1,123.90