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	$54.73	4.169%	$57.0117	$57.01	$57.00	$57.00
Purchase #2	$240.79	13.657%	$273.6747	$273.67	$273.65	$273.70
Purchase #3	$77.51	6.321%	$82.4094	$82.41	$82.40	$82.40
Purchase #4	$147.77	13.822%	$168.1948	$168.19	$168.20	$168.20
Purchase #5	$34.42	5.792%	$36.4136	$36.41	$36.40	$36.40
Purchase #6	$18.65	13.142%	$21.101	$21.10	$21.10	$21.10
Purchase #7	$65.51	12.749%	$73.8619	$73.86	$73.85	$73.90
7 purchase totals =	$639.38		$712.6671	$712.65	$712.60	$712.70