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	$169.81	6.417%	$180.7067	$180.71	$180.70	$180.70
Purchase #2	$120.72	6.289%	$128.3121	$128.31	$128.30	$128.30
Purchase #3	$132.36	6.766%	$141.3155	$141.32	$141.30	$141.30
Purchase #4	$67.94	13.345%	$77.0066	$77.01	$77.00	$77.00
Purchase #5	$250.92	13.377%	$284.4856	$284.49	$284.50	$284.50
Purchase #6	$37.35	3.203%	$38.5463	$38.55	$38.55	$38.50
Purchase #7	$50.69	3.760%	$52.5959	$52.60	$52.60	$52.60
7 purchase totals =	$829.79		$902.9687	$902.99	$902.95	$902.90