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	$90.83	10.137%	$100.0374	$100.04	$100.05	$100.00
Purchase #2	$167.61	11.353%	$186.6388	$186.64	$186.65	$186.60
Purchase #3	$39.66	6.484%	$42.2316	$42.23	$42.25	$42.20
Purchase #4	$81.47	13.588%	$92.5401	$92.54	$92.55	$92.50
Purchase #5	$142.54	12.325%	$160.1081	$160.11	$160.10	$160.10
Purchase #6	$233.75	10.657%	$258.6607	$258.66	$258.65	$258.70
Purchase #7	$10.44	7.244%	$11.1963	$11.20	$11.20	$11.20
7 purchase totals =	$766.30		$851.4130	$851.42	$851.45	$851.30