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	$27.56	13.217%	$31.2026	$31.20	$31.20	$31.20
Purchase #2	$73.70	12.354%	$82.8049	$82.80	$82.80	$82.80
Purchase #3	$29.53	6.364%	$31.4093	$31.41	$31.40	$31.40
Purchase #4	$238.32	6.789%	$254.4995	$254.50	$254.50	$254.50
Purchase #5	$241.72	12.291%	$271.4298	$271.43	$271.45	$271.40
Purchase #6	$159.55	3.509%	$165.1486	$165.15	$165.15	$165.10
Purchase #7	$93.81	7.379%	$100.7322	$100.73	$100.75	$100.70
7 purchase totals =	$864.19		$937.2269	$937.22	$937.25	$937.10