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	$156.92	6.623%	$167.3128	$167.31	$167.30	$167.30
Purchase #2	$125.62	4.792%	$131.6397	$131.64	$131.65	$131.60
Purchase #3	$131.82	12.633%	$148.4728	$148.47	$148.45	$148.50
Purchase #4	$30.92	9.136%	$33.7449	$33.74	$33.75	$33.70
Purchase #5	$207.68	4.590%	$217.2125	$217.21	$217.20	$217.20
Purchase #6	$82.88	10.127%	$91.2733	$91.27	$91.25	$91.30
Purchase #7	$118.31	7.579%	$127.2767	$127.28	$127.30	$127.30
7 purchase totals =	$854.15		$916.9327	$916.92	$916.90	$916.90