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	$94.29	6.187%	$100.1237	$100.12	$100.10	$100.10
Purchase #2	$188.69	5.784%	$199.6038	$199.60	$199.60	$199.60
Purchase #3	$207.66	8.550%	$225.4149	$225.41	$225.40	$225.40
Purchase #4	$143.43	4.304%	$149.6032	$149.60	$149.60	$149.60
Purchase #5	$124.34	10.794%	$137.7613	$137.76	$137.75	$137.80
Purchase #6	$57.35	8.296%	$62.1078	$62.11	$62.10	$62.10
Purchase #7	$55.56	6.720%	$59.2936	$59.29	$59.30	$59.30
7 purchase totals =	$871.32		$933.9083	$933.89	$933.85	$933.90