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	$70.28	8.832%	$76.4871	$76.49	$76.50	$76.50
Purchase #2	$60.41	5.345%	$63.6389	$63.64	$63.65	$63.60
Purchase #3	$74.87	5.196%	$78.7602	$78.76	$78.75	$78.80
Purchase #4	$225.80	11.430%	$251.6089	$251.61	$251.60	$251.60
Purchase #5	$134.88	8.256%	$146.0157	$146.02	$146.00	$146.00
Purchase #6	$93.85	6.315%	$99.7766	$99.78	$99.80	$99.80
Purchase #7	$196.89	8.612%	$213.8462	$213.85	$213.85	$213.80
7 purchase totals =	$856.98		$930.1336	$930.15	$930.15	$930.10