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	$80.68	12.141%	$90.4754	$90.48	$90.50	$90.50
Purchase #2	$164.89	9.567%	$180.665	$180.67	$180.65	$180.70
Purchase #3	$123.80	6.458%	$131.795	$131.80	$131.80	$131.80
Purchase #4	$152.71	4.391%	$159.4155	$159.42	$159.40	$159.40
Purchase #5	$11.55	11.325%	$12.858	$12.86	$12.85	$12.90
Purchase #6	$134.77	12.284%	$151.3251	$151.33	$151.35	$151.30
Purchase #7	$65.32	5.687%	$69.0347	$69.03	$69.05	$69.00
7 purchase totals =	$733.72		$795.5687	$795.59	$795.60	$795.60