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	$46.44	9.321%	$50.7687	$50.77	$50.75	$50.80
Purchase #2	$63.49	5.744%	$67.1369	$67.14	$67.15	$67.10
Purchase #3	$55.80	12.629%	$62.847	$62.85	$62.85	$62.80
Purchase #4	$95.72	5.854%	$101.3234	$101.32	$101.30	$101.30
Purchase #5	$54.62	10.805%	$60.5217	$60.52	$60.50	$60.50
Purchase #6	$23.26	9.140%	$25.386	$25.39	$25.40	$25.40
Purchase #7	$35.46	6.548%	$37.7819	$37.78	$37.80	$37.80
7 purchase totals =	$374.79		$405.7656	$405.77	$405.75	$405.70