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	$223.40	8.380%	$242.1209	$242.12	$242.10	$242.10
Purchase #2	$153.36	8.441%	$166.3051	$166.31	$166.30	$166.30
Purchase #3	$122.40	13.219%	$138.5801	$138.58	$138.60	$138.60
Purchase #4	$242.57	8.866%	$264.0763	$264.08	$264.10	$264.10
Purchase #5	$92.41	10.714%	$102.3108	$102.31	$102.30	$102.30
Purchase #6	$31.43	5.829%	$33.2621	$33.26	$33.25	$33.30
Purchase #7	$137.25	11.340%	$152.8142	$152.81	$152.80	$152.80
7 purchase totals =	$1,002.82		$1,099.4695	$1,099.47	$1,099.45	$1,099.50