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	$156.44	12.364%	$175.7822	$175.78	$175.80	$175.80
Purchase #2	$142.94	5.557%	$150.8832	$150.88	$150.90	$150.90
Purchase #3	$128.60	10.386%	$141.9564	$141.96	$141.95	$142.00
Purchase #4	$60.60	4.481%	$63.3155	$63.32	$63.30	$63.30
Purchase #5	$130.90	5.271%	$137.7997	$137.80	$137.80	$137.80
Purchase #6	$70.55	10.617%	$78.0403	$78.04	$78.05	$78.00
Purchase #7	$99.78	9.109%	$108.869	$108.87	$108.85	$108.90
7 purchase totals =	$789.81		$856.6463	$856.65	$856.65	$856.70