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	$81.28	9.582%	$89.0682	$89.07	$89.05	$89.10
Purchase #2	$182.33	9.328%	$199.3377	$199.34	$199.35	$199.30
Purchase #3	$89.54	11.657%	$99.9777	$99.98	$100.00	$100.00
Purchase #4	$128.37	4.390%	$134.0054	$134.01	$134.00	$134.00
Purchase #5	$137.40	12.710%	$154.8635	$154.86	$154.85	$154.90
Purchase #6	$108.34	13.172%	$122.6105	$122.61	$122.60	$122.60
Purchase #7	$238.74	3.815%	$247.8479	$247.85	$247.85	$247.80
7 purchase totals =	$966.00		$1,047.7109	$1,047.72	$1,047.70	$1,047.70