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	$197.81	12.718%	$222.9675	$222.97	$222.95	$223.00
Purchase #2	$41.51	9.687%	$45.5311	$45.53	$45.55	$45.50
Purchase #3	$235.75	4.679%	$246.7807	$246.78	$246.80	$246.80
Purchase #4	$126.32	6.383%	$134.383	$134.38	$134.40	$134.40
Purchase #5	$178.85	3.819%	$185.6803	$185.68	$185.70	$185.70
Purchase #6	$67.72	12.104%	$75.9168	$75.92	$75.90	$75.90
Purchase #7	$71.47	10.209%	$78.7664	$78.77	$78.75	$78.80
7 purchase totals =	$919.43		$990.0258	$990.03	$990.05	$990.10