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	$26.94	6.624%	$28.7245	$28.72	$28.70	$28.70
Purchase #2	$175.36	9.260%	$191.5983	$191.60	$191.60	$191.60
Purchase #3	$175.33	3.574%	$181.5963	$181.60	$181.60	$181.60
Purchase #4	$89.32	12.692%	$100.6565	$100.66	$100.65	$100.70
Purchase #5	$56.76	10.208%	$62.5541	$62.55	$62.55	$62.60
Purchase #6	$72.86	8.290%	$78.9001	$78.90	$78.90	$78.90
Purchase #7	$88.66	5.871%	$93.8652	$93.87	$93.85	$93.90
7 purchase totals =	$685.23		$737.8950	$737.90	$737.85	$738.00