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	$154.91	8.654%	$168.3159	$168.32	$168.30	$168.30
Purchase #2	$89.93	4.672%	$94.1315	$94.13	$94.15	$94.10
Purchase #3	$80.96	10.211%	$89.2268	$89.23	$89.25	$89.20
Purchase #4	$112.34	7.446%	$120.7048	$120.70	$120.70	$120.70
Purchase #5	$151.94	12.254%	$170.5587	$170.56	$170.55	$170.60
Purchase #6	$168.92	8.584%	$183.4201	$183.42	$183.40	$183.40
Purchase #7	$91.28	9.632%	$100.0721	$100.07	$100.05	$100.10
7 purchase totals =	$850.28		$926.4299	$926.43	$926.40	$926.40