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	$150.69	5.182%	$158.4988	$158.50	$158.50	$158.50
Purchase #2	$93.27	4.738%	$97.6891	$97.69	$97.70	$97.70
Purchase #3	$184.56	5.415%	$194.5539	$194.55	$194.55	$194.60
Purchase #4	$79.48	4.326%	$82.9183	$82.92	$82.90	$82.90
Purchase #5	$168.61	9.730%	$185.0158	$185.02	$185.00	$185.00
Purchase #6	$140.94	5.771%	$149.0736	$149.07	$149.05	$149.10
Purchase #7	$40.87	3.826%	$42.4337	$42.43	$42.45	$42.40
7 purchase totals =	$858.42		$910.1832	$910.18	$910.15	$910.20