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	$64.26	6.233%	$68.2653	$68.27	$68.25	$68.30
Purchase #2	$147.35	5.750%	$155.8226	$155.82	$155.80	$155.80
Purchase #3	$159.86	7.739%	$172.2316	$172.23	$172.25	$172.20
Purchase #4	$245.25	12.231%	$275.2465	$275.25	$275.25	$275.20
Purchase #5	$134.31	10.623%	$148.5778	$148.58	$148.60	$148.60
Purchase #6	$99.61	7.723%	$107.3029	$107.30	$107.30	$107.30
Purchase #7	$71.87	12.553%	$80.8918	$80.89	$80.90	$80.90
7 purchase totals =	$922.51		$1,008.3385	$1,008.34	$1,008.35	$1,008.30