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	$106.33	12.744%	$119.8807	$119.88	$119.90	$119.90
Purchase #2	$41.51	8.776%	$45.1529	$45.15	$45.15	$45.20
Purchase #3	$20.95	4.382%	$21.868	$21.87	$21.85	$21.90
Purchase #4	$187.75	6.475%	$199.9068	$199.91	$199.90	$199.90
Purchase #5	$152.69	11.289%	$169.9272	$169.93	$169.95	$169.90
Purchase #6	$17.90	3.810%	$18.582	$18.58	$18.60	$18.60
Purchase #7	$151.74	9.720%	$166.4891	$166.49	$166.50	$166.50
7 purchase totals =	$678.87		$741.8067	$741.81	$741.85	$741.90