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	$240.98	6.471%	$256.5738	$256.57	$256.55	$256.60
Purchase #2	$111.89	11.820%	$125.1154	$125.12	$125.10	$125.10
Purchase #3	$180.47	8.843%	$196.429	$196.43	$196.45	$196.40
Purchase #4	$41.49	11.539%	$46.2775	$46.28	$46.30	$46.30
Purchase #5	$24.52	7.408%	$26.3364	$26.34	$26.35	$26.30
Purchase #6	$101.71	10.342%	$112.2288	$112.23	$112.25	$112.20
Purchase #7	$148.85	12.166%	$166.9591	$166.96	$166.95	$167.00
7 purchase totals =	$849.91		$929.9200	$929.93	$929.95	$929.90