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	$221.61	9.605%	$242.8956	$242.90	$242.90	$242.90
Purchase #2	$233.69	3.180%	$241.1213	$241.12	$241.10	$241.10
Purchase #3	$177.74	10.744%	$196.8364	$196.84	$196.85	$196.80
Purchase #4	$160.59	13.204%	$181.7943	$181.79	$181.80	$181.80
Purchase #5	$27.74	9.382%	$30.3426	$30.34	$30.35	$30.30
Purchase #6	$82.56	9.817%	$90.6649	$90.66	$90.65	$90.70
Purchase #7	$176.81	6.217%	$187.8023	$187.80	$187.80	$187.80
7 purchase totals =	$1,080.74		$1,171.4574	$1,171.45	$1,171.45	$1,171.40