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	$100.81	13.326%	$114.2439	$114.24	$114.25	$114.20
Purchase #2	$107.46	8.623%	$116.7263	$116.73	$116.75	$116.70
Purchase #3	$83.39	7.765%	$89.8652	$89.87	$89.85	$89.90
Purchase #4	$119.34	7.422%	$128.1974	$128.20	$128.20	$128.20
Purchase #5	$77.58	3.381%	$80.203	$80.20	$80.20	$80.20
Purchase #6	$55.50	7.615%	$59.7263	$59.73	$59.75	$59.70
Purchase #7	$216.98	5.766%	$229.4911	$229.49	$229.50	$229.50
7 purchase totals =	$761.06		$818.4532	$818.46	$818.50	$818.40