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	$85.33	6.122%	$90.5539	$90.55	$90.55	$90.60
Purchase #2	$170.67	13.163%	$193.1353	$193.14	$193.15	$193.10
Purchase #3	$123.58	7.693%	$133.087	$133.09	$133.10	$133.10
Purchase #4	$63.50	3.109%	$65.4742	$65.47	$65.45	$65.50
Purchase #5	$33.94	11.468%	$37.8322	$37.83	$37.85	$37.80
Purchase #6	$40.39	9.496%	$44.2254	$44.23	$44.25	$44.20
Purchase #7	$122.62	9.155%	$133.8459	$133.85	$133.85	$133.80
7 purchase totals =	$640.03		$698.1539	$698.16	$698.20	$698.10