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	$143.33	10.512%	$158.3968	$158.40	$158.40	$158.40
Purchase #2	$91.43	13.559%	$103.827	$103.83	$103.85	$103.80
Purchase #3	$123.88	8.498%	$134.4073	$134.41	$134.40	$134.40
Purchase #4	$166.46	5.677%	$175.9099	$175.91	$175.90	$175.90
Purchase #5	$222.52	4.220%	$231.9103	$231.91	$231.90	$231.90
Purchase #6	$245.37	12.411%	$275.8229	$275.82	$275.80	$275.80
Purchase #7	$127.28	5.345%	$134.0831	$134.08	$134.10	$134.10
7 purchase totals =	$1,120.27		$1,214.3573	$1,214.36	$1,214.35	$1,214.30