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	$18.96	6.313%	$20.1569	$20.16	$20.15	$20.20
Purchase #2	$130.27	11.480%	$145.225	$145.23	$145.25	$145.20
Purchase #3	$12.65	7.505%	$13.5994	$13.60	$13.60	$13.60
Purchase #4	$39.87	6.575%	$42.4915	$42.49	$42.50	$42.50
Purchase #5	$189.92	13.414%	$215.3959	$215.40	$215.40	$215.40
Purchase #6	$141.63	11.667%	$158.154	$158.15	$158.15	$158.20
Purchase #7	$152.82	12.108%	$171.3234	$171.32	$171.30	$171.30
7 purchase totals =	$686.12		$766.3461	$766.35	$766.35	$766.40