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	$98.71	4.823%	$103.4708	$103.47	$103.45	$103.50
Purchase #2	$133.71	12.120%	$149.9157	$149.92	$149.90	$149.90
Purchase #3	$129.68	9.724%	$142.2901	$142.29	$142.30	$142.30
Purchase #4	$154.72	7.676%	$166.5963	$166.60	$166.60	$166.60
Purchase #5	$54.25	10.205%	$59.7862	$59.79	$59.80	$59.80
Purchase #6	$79.93	8.135%	$86.4323	$86.43	$86.45	$86.40
Purchase #7	$178.34	3.320%	$184.2609	$184.26	$184.25	$184.30
7 purchase totals =	$829.34		$892.7523	$892.76	$892.75	$892.80