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	$72.53	6.573%	$77.2974	$77.30	$77.30	$77.30
Purchase #2	$11.89	12.244%	$13.3458	$13.35	$13.35	$13.30
Purchase #3	$198.44	6.212%	$210.7671	$210.77	$210.75	$210.80
Purchase #4	$142.52	3.566%	$147.6023	$147.60	$147.60	$147.60
Purchase #5	$36.77	5.816%	$38.9085	$38.91	$38.90	$38.90
Purchase #6	$104.83	6.623%	$111.7729	$111.77	$111.75	$111.80
Purchase #7	$7.66	8.766%	$8.3315	$8.33	$8.35	$8.30
7 purchase totals =	$574.64		$608.0255	$608.03	$608.00	$608.00