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	$29.70	8.401%	$32.1951	$32.20	$32.20	$32.20
Purchase #2	$146.27	6.443%	$155.6942	$155.69	$155.70	$155.70
Purchase #3	$187.91	6.605%	$200.3215	$200.32	$200.30	$200.30
Purchase #4	$127.31	9.311%	$139.1638	$139.16	$139.15	$139.20
Purchase #5	$213.86	9.154%	$233.4367	$233.44	$233.45	$233.40
Purchase #6	$135.79	11.114%	$150.8817	$150.88	$150.90	$150.90
Purchase #7	$26.77	10.433%	$29.5629	$29.56	$29.55	$29.60
7 purchase totals =	$867.61		$941.2559	$941.25	$941.25	$941.30