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	$18.44	10.234%	$20.3271	$20.33	$20.35	$20.30
Purchase #2	$116.43	5.714%	$123.0828	$123.08	$123.10	$123.10
Purchase #3	$78.38	12.495%	$88.1736	$88.17	$88.15	$88.20
Purchase #4	$116.54	13.119%	$131.8289	$131.83	$131.85	$131.80
Purchase #5	$105.44	13.325%	$119.4899	$119.49	$119.50	$119.50
Purchase #6	$7.56	7.717%	$8.1434	$8.14	$8.15	$8.10
Purchase #7	$79.55	5.658%	$84.0509	$84.05	$84.05	$84.10
7 purchase totals =	$522.34		$575.0966	$575.09	$575.15	$575.10