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	$41.66	6.563%	$44.3941	$44.39	$44.40	$44.40
Purchase #2	$123.79	12.556%	$139.3331	$139.33	$139.35	$139.30
Purchase #3	$191.33	7.506%	$205.6912	$205.69	$205.70	$205.70
Purchase #4	$147.61	5.716%	$156.0474	$156.05	$156.05	$156.00
Purchase #5	$76.89	11.188%	$85.4925	$85.49	$85.50	$85.50
Purchase #6	$100.78	10.736%	$111.5997	$111.60	$111.60	$111.60
Purchase #7	$41.42	13.251%	$46.9086	$46.91	$46.90	$46.90
7 purchase totals =	$723.48		$789.4666	$789.46	$789.50	$789.40