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	$176.35	7.754%	$190.0242	$190.02	$190.00	$190.00
Purchase #2	$139.97	13.226%	$158.4824	$158.48	$158.50	$158.50
Purchase #3	$69.99	10.621%	$77.4236	$77.42	$77.40	$77.40
Purchase #4	$113.37	5.646%	$119.7709	$119.77	$119.75	$119.80
Purchase #5	$115.79	13.680%	$131.6301	$131.63	$131.65	$131.60
Purchase #6	$120.63	8.600%	$131.0042	$131.00	$131.00	$131.00
Purchase #7	$185.81	4.732%	$194.6025	$194.60	$194.60	$194.60
7 purchase totals =	$921.91		$1,002.9379	$1,002.92	$1,002.90	$1,002.90