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	$67.59	6.202%	$71.7819	$71.78	$71.80	$71.80
Purchase #2	$220.97	9.345%	$241.6196	$241.62	$241.60	$241.60
Purchase #3	$183.62	6.815%	$196.1337	$196.13	$196.15	$196.10
Purchase #4	$48.35	11.403%	$53.8634	$53.86	$53.85	$53.90
Purchase #5	$98.83	5.361%	$104.1283	$104.13	$104.15	$104.10
Purchase #6	$149.56	7.259%	$160.4166	$160.42	$160.40	$160.40
Purchase #7	$69.89	7.167%	$74.899	$74.90	$74.90	$74.90
7 purchase totals =	$838.81		$902.8425	$902.84	$902.85	$902.80