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	$151.25	11.229%	$168.2339	$168.23	$168.25	$168.20
Purchase #2	$129.33	3.469%	$133.8165	$133.82	$133.80	$133.80
Purchase #3	$100.76	6.792%	$107.6036	$107.60	$107.60	$107.60
Purchase #4	$173.69	3.444%	$179.6719	$179.67	$179.65	$179.70
Purchase #5	$137.50	12.367%	$154.5046	$154.50	$154.50	$154.50
Purchase #6	$90.81	9.432%	$99.3752	$99.38	$99.40	$99.40
Purchase #7	$10.71	7.788%	$11.5441	$11.54	$11.55	$11.50
7 purchase totals =	$794.05		$854.7498	$854.74	$854.75	$854.70