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	$70.71	10.375%	$78.0462	$78.05	$78.05	$78.00
Purchase #2	$61.89	4.606%	$64.7407	$64.74	$64.75	$64.70
Purchase #3	$43.60	6.760%	$46.5474	$46.55	$46.55	$46.50
Purchase #4	$49.67	6.655%	$52.9755	$52.98	$53.00	$53.00
Purchase #5	$228.72	13.704%	$260.0638	$260.06	$260.05	$260.10
Purchase #6	$136.32	12.609%	$153.5086	$153.51	$153.50	$153.50
Purchase #7	$55.45	4.354%	$57.8643	$57.86	$57.85	$57.90
7 purchase totals =	$646.36		$713.7465	$713.75	$713.75	$713.70