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	$36.29	8.519%	$39.3815	$39.38	$39.40	$39.40
Purchase #2	$147.48	12.677%	$166.176	$166.18	$166.20	$166.20
Purchase #3	$151.33	3.624%	$156.8142	$156.81	$156.80	$156.80
Purchase #4	$96.53	8.828%	$105.0517	$105.05	$105.05	$105.10
Purchase #5	$31.82	11.243%	$35.3975	$35.40	$35.40	$35.40
Purchase #6	$187.32	4.866%	$196.435	$196.44	$196.45	$196.40
Purchase #7	$96.33	10.698%	$106.6354	$106.64	$106.65	$106.60
7 purchase totals =	$747.10		$805.8913	$805.90	$805.95	$805.90