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	$156.98	9.645%	$172.1207	$172.12	$172.10	$172.10
Purchase #2	$218.37	11.673%	$243.8603	$243.86	$243.85	$243.90
Purchase #3	$130.44	11.599%	$145.5697	$145.57	$145.55	$145.60
Purchase #4	$18.41	12.426%	$20.6976	$20.70	$20.70	$20.70
Purchase #5	$103.37	13.393%	$117.2143	$117.21	$117.20	$117.20
Purchase #6	$120.70	5.465%	$127.2963	$127.30	$127.30	$127.30
Purchase #7	$235.89	7.589%	$253.7917	$253.79	$253.80	$253.80
7 purchase totals =	$984.16		$1,080.5506	$1,080.55	$1,080.50	$1,080.60