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	$212.53	8.371%	$230.3209	$230.32	$230.30	$230.30
Purchase #2	$114.93	7.308%	$123.3291	$123.33	$123.35	$123.30
Purchase #3	$230.65	10.397%	$254.6307	$254.63	$254.65	$254.60
Purchase #4	$38.39	9.661%	$42.0989	$42.10	$42.10	$42.10
Purchase #5	$11.76	10.157%	$12.9545	$12.95	$12.95	$13.00
Purchase #6	$103.32	10.831%	$114.5106	$114.51	$114.50	$114.50
Purchase #7	$25.42	12.125%	$28.5022	$28.50	$28.50	$28.50
7 purchase totals =	$737.00		$806.3469	$806.34	$806.35	$806.30