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	$25.89	9.744%	$28.4127	$28.41	$28.40	$28.40
Purchase #2	$21.67	13.358%	$24.5647	$24.56	$24.55	$24.60
Purchase #3	$111.82	13.692%	$127.1304	$127.13	$127.15	$127.10
Purchase #4	$103.60	9.489%	$113.4306	$113.43	$113.45	$113.40
Purchase #5	$115.33	10.128%	$127.0106	$127.01	$127.00	$127.00
Purchase #6	$83.72	10.827%	$92.7844	$92.78	$92.80	$92.80
Purchase #7	$30.43	3.821%	$31.5927	$31.59	$31.60	$31.60
7 purchase totals =	$492.46		$544.9261	$544.91	$544.95	$544.90