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	$58.32	12.178%	$65.4222	$65.42	$65.40	$65.40
Purchase #2	$65.47	9.538%	$71.7145	$71.71	$71.70	$71.70
Purchase #3	$173.66	10.860%	$192.5195	$192.52	$192.50	$192.50
Purchase #4	$160.61	13.802%	$182.7774	$182.78	$182.80	$182.80
Purchase #5	$100.74	3.444%	$104.2095	$104.21	$104.20	$104.20
Purchase #6	$116.53	7.187%	$124.905	$124.91	$124.90	$124.90
Purchase #7	$98.92	6.759%	$105.606	$105.61	$105.60	$105.60
7 purchase totals =	$774.25		$847.1541	$847.16	$847.10	$847.10