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	$106.94	13.437%	$121.3095	$121.31	$121.30	$121.30
Purchase #2	$223.75	6.790%	$238.9426	$238.94	$238.95	$238.90
Purchase #3	$151.63	10.644%	$167.7695	$167.77	$167.75	$167.80
Purchase #4	$123.30	12.691%	$138.948	$138.95	$138.95	$138.90
Purchase #5	$88.56	11.859%	$99.0623	$99.06	$99.05	$99.10
Purchase #6	$57.30	4.583%	$59.9261	$59.93	$59.95	$59.90
Purchase #7	$58.55	3.465%	$60.5788	$60.58	$60.60	$60.60
7 purchase totals =	$810.03		$886.5368	$886.54	$886.55	$886.50