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	$120.47	9.129%	$131.4677	$131.47	$131.45	$131.50
Purchase #2	$127.29	8.244%	$137.7838	$137.78	$137.80	$137.80
Purchase #3	$33.32	13.801%	$37.9185	$37.92	$37.90	$37.90
Purchase #4	$160.49	5.146%	$168.7488	$168.75	$168.75	$168.70
Purchase #5	$166.45	13.157%	$188.3498	$188.35	$188.35	$188.30
Purchase #6	$138.82	8.149%	$150.1324	$150.13	$150.15	$150.10
Purchase #7	$96.95	13.142%	$109.6912	$109.69	$109.70	$109.70
7 purchase totals =	$843.79		$924.0922	$924.09	$924.10	$924.00