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	$128.75	13.867%	$146.6038	$146.60	$146.60	$146.60
Purchase #2	$225.41	10.752%	$249.6461	$249.65	$249.65	$249.60
Purchase #3	$167.60	10.419%	$185.0622	$185.06	$185.05	$185.10
Purchase #4	$95.98	3.762%	$99.5908	$99.59	$99.60	$99.60
Purchase #5	$136.90	12.417%	$153.8989	$153.90	$153.90	$153.90
Purchase #6	$185.44	3.730%	$192.3569	$192.36	$192.35	$192.40
Purchase #7	$212.43	12.423%	$238.8202	$238.82	$238.80	$238.80
7 purchase totals =	$1,152.51		$1,265.9789	$1,265.98	$1,265.95	$1,266.00