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	$190.40	13.710%	$216.5038	$216.50	$216.50	$216.50
Purchase #2	$55.49	11.403%	$61.8175	$61.82	$61.80	$61.80
Purchase #3	$225.49	3.484%	$233.3461	$233.35	$233.35	$233.30
Purchase #4	$48.63	6.713%	$51.8945	$51.89	$51.90	$51.90
Purchase #5	$51.94	4.235%	$54.1397	$54.14	$54.15	$54.10
Purchase #6	$233.77	9.200%	$255.2768	$255.28	$255.30	$255.30
Purchase #7	$68.42	7.698%	$73.687	$73.69	$73.70	$73.70
7 purchase totals =	$874.14		$946.6654	$946.67	$946.70	$946.60