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	$103.72	9.251%	$113.3151	$113.32	$113.30	$113.30
Purchase #2	$168.77	12.815%	$190.3979	$190.40	$190.40	$190.40
Purchase #3	$238.73	13.861%	$271.8204	$271.82	$271.80	$271.80
Purchase #4	$113.56	8.364%	$123.0582	$123.06	$123.05	$123.10
Purchase #5	$220.84	5.737%	$233.5096	$233.51	$233.50	$233.50
Purchase #6	$184.89	6.487%	$196.8838	$196.88	$196.90	$196.90
Purchase #7	$194.29	3.228%	$200.5617	$200.56	$200.55	$200.60
7 purchase totals =	$1,224.80		$1,329.5467	$1,329.55	$1,329.50	$1,329.60