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	$140.39	8.122%	$151.7925	$151.79	$151.80	$151.80
Purchase #2	$211.56	10.660%	$234.1123	$234.11	$234.10	$234.10
Purchase #3	$55.51	13.223%	$62.8501	$62.85	$62.85	$62.90
Purchase #4	$164.52	4.677%	$172.2146	$172.21	$172.20	$172.20
Purchase #5	$71.32	4.741%	$74.7013	$74.70	$74.70	$74.70
Purchase #6	$180.82	8.667%	$196.4917	$196.49	$196.50	$196.50
Purchase #7	$27.37	8.109%	$29.5894	$29.59	$29.60	$29.60
7 purchase totals =	$851.49		$921.7519	$921.74	$921.75	$921.80