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	$72.58	6.213%	$77.0894	$77.09	$77.10	$77.10
Purchase #2	$72.32	5.592%	$76.3641	$76.36	$76.35	$76.40
Purchase #3	$197.50	3.804%	$205.0129	$205.01	$205.00	$205.00
Purchase #4	$46.76	8.763%	$50.8576	$50.86	$50.85	$50.90
Purchase #5	$185.82	5.714%	$196.4378	$196.44	$196.45	$196.40
Purchase #6	$85.61	5.378%	$90.2141	$90.21	$90.20	$90.20
Purchase #7	$247.52	12.102%	$277.4749	$277.47	$277.45	$277.50
7 purchase totals =	$908.11		$973.4508	$973.44	$973.40	$973.50