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	$168.34	6.227%	$178.8225	$178.82	$178.80	$178.80
Purchase #2	$135.86	11.658%	$151.6986	$151.70	$151.70	$151.70
Purchase #3	$139.96	13.234%	$158.4823	$158.48	$158.50	$158.50
Purchase #4	$54.96	11.561%	$61.3139	$61.31	$61.30	$61.30
Purchase #5	$89.26	12.422%	$100.3479	$100.35	$100.35	$100.30
Purchase #6	$137.78	6.403%	$146.6021	$146.60	$146.60	$146.60
Purchase #7	$170.83	10.803%	$189.2848	$189.28	$189.30	$189.30
7 purchase totals =	$896.99		$986.5521	$986.54	$986.55	$986.50