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	$35.69	13.176%	$40.3925	$40.39	$40.40	$40.40
Purchase #2	$123.81	3.347%	$127.9539	$127.95	$127.95	$128.00
Purchase #3	$139.59	9.122%	$152.3234	$152.32	$152.30	$152.30
Purchase #4	$27.58	13.364%	$31.2658	$31.27	$31.25	$31.30
Purchase #5	$237.26	6.810%	$253.4174	$253.42	$253.40	$253.40
Purchase #6	$61.54	9.142%	$67.166	$67.17	$67.15	$67.20
Purchase #7	$108.86	3.596%	$112.7746	$112.77	$112.75	$112.80
7 purchase totals =	$734.33		$785.2936	$785.29	$785.20	$785.40