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	$91.41	10.838%	$101.317	$101.32	$101.30	$101.30
Purchase #2	$100.73	7.653%	$108.4389	$108.44	$108.45	$108.40
Purchase #3	$137.72	8.840%	$149.8944	$149.89	$149.90	$149.90
Purchase #4	$249.69	13.794%	$284.1322	$284.13	$284.15	$284.10
Purchase #5	$48.82	7.787%	$52.6216	$52.62	$52.60	$52.60
Purchase #6	$179.28	11.537%	$199.9635	$199.96	$199.95	$200.00
Purchase #7	$86.89	3.257%	$89.72	$89.72	$89.70	$89.70
7 purchase totals =	$894.54		$986.0876	$986.08	$986.05	$986.00