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	$145.85	3.869%	$151.4929	$151.49	$151.50	$151.50
Purchase #2	$126.79	4.378%	$132.3409	$132.34	$132.35	$132.30
Purchase #3	$38.54	13.647%	$43.7996	$43.80	$43.80	$43.80
Purchase #4	$80.77	10.622%	$89.3494	$89.35	$89.35	$89.30
Purchase #5	$94.90	4.527%	$99.1961	$99.20	$99.20	$99.20
Purchase #6	$88.38	3.794%	$91.7331	$91.73	$91.75	$91.70
Purchase #7	$66.88	10.229%	$73.7212	$73.72	$73.70	$73.70
7 purchase totals =	$642.11		$681.6332	$681.63	$681.65	$681.50