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	$121.28	7.817%	$130.7605	$130.76	$130.75	$130.80
Purchase #2	$38.73	9.359%	$42.3547	$42.35	$42.35	$42.40
Purchase #3	$29.52	12.719%	$33.2746	$33.27	$33.25	$33.30
Purchase #4	$53.98	9.558%	$59.1394	$59.14	$59.15	$59.10
Purchase #5	$181.50	7.857%	$195.7605	$195.76	$195.75	$195.80
Purchase #6	$10.56	5.713%	$11.1633	$11.16	$11.15	$11.20
Purchase #7	$106.94	12.414%	$120.2155	$120.22	$120.20	$120.20
7 purchase totals =	$542.51		$592.6685	$592.66	$592.60	$592.80