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	$67.92	4.120%	$70.7183	$70.72	$70.70	$70.70
Purchase #2	$124.52	3.143%	$128.4337	$128.43	$128.45	$128.40
Purchase #3	$153.34	9.858%	$168.4563	$168.46	$168.45	$168.50
Purchase #4	$80.88	7.333%	$86.8109	$86.81	$86.80	$86.80
Purchase #5	$113.98	11.499%	$127.0866	$127.09	$127.10	$127.10
Purchase #6	$117.54	9.700%	$128.9414	$128.94	$128.95	$128.90
Purchase #7	$198.96	7.634%	$214.1486	$214.15	$214.15	$214.10
7 purchase totals =	$857.14		$924.5958	$924.60	$924.60	$924.50