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	$172.28	8.871%	$187.563	$187.56	$187.55	$187.60
Purchase #2	$141.92	13.470%	$161.0366	$161.04	$161.05	$161.00
Purchase #3	$50.34	12.410%	$56.5872	$56.59	$56.60	$56.60
Purchase #4	$218.71	6.691%	$233.3439	$233.34	$233.35	$233.30
Purchase #5	$79.72	8.353%	$86.379	$86.38	$86.40	$86.40
Purchase #6	$45.46	12.686%	$51.2271	$51.23	$51.25	$51.20
Purchase #7	$30.47	10.470%	$33.6602	$33.66	$33.65	$33.70
7 purchase totals =	$738.90		$809.7970	$809.80	$809.85	$809.80