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	$249.89	12.768%	$281.796	$281.80	$281.80	$281.80
Purchase #2	$50.88	7.282%	$54.5851	$54.59	$54.60	$54.60
Purchase #3	$95.43	4.734%	$99.9477	$99.95	$99.95	$99.90
Purchase #4	$49.28	3.105%	$50.8101	$50.81	$50.80	$50.80
Purchase #5	$80.76	5.396%	$85.1178	$85.12	$85.10	$85.10
Purchase #6	$90.80	3.390%	$93.8781	$93.88	$93.90	$93.90
Purchase #7	$226.98	10.756%	$251.394	$251.39	$251.40	$251.40
7 purchase totals =	$844.02		$917.5288	$917.54	$917.55	$917.50