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	$101.82	3.183%	$105.0609	$105.06	$105.05	$105.10
Purchase #2	$112.82	9.578%	$123.6259	$123.63	$123.65	$123.60
Purchase #3	$234.25	6.708%	$249.9635	$249.96	$249.95	$250.00
Purchase #4	$139.86	5.534%	$147.5999	$147.60	$147.60	$147.60
Purchase #5	$222.80	9.651%	$244.3024	$244.30	$244.30	$244.30
Purchase #6	$18.73	4.271%	$19.53	$19.53	$19.55	$19.50
Purchase #7	$57.62	13.510%	$65.4045	$65.40	$65.40	$65.40
7 purchase totals =	$887.90		$955.4871	$955.48	$955.50	$955.50