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	$107.25	10.843%	$118.8791	$118.88	$118.90	$118.90
Purchase #2	$123.45	11.590%	$137.7579	$137.76	$137.75	$137.80
Purchase #3	$97.42	8.766%	$105.9598	$105.96	$105.95	$106.00
Purchase #4	$78.28	10.274%	$86.3225	$86.32	$86.30	$86.30
Purchase #5	$44.61	5.609%	$47.1122	$47.11	$47.10	$47.10
Purchase #6	$225.35	13.795%	$256.437	$256.44	$256.45	$256.40
Purchase #7	$108.30	11.185%	$120.4134	$120.41	$120.40	$120.40
7 purchase totals =	$784.66		$872.8819	$872.88	$872.85	$872.90