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	$38.85	10.387%	$42.8853	$42.89	$42.90	$42.90
Purchase #2	$208.33	4.313%	$217.3153	$217.32	$217.30	$217.30
Purchase #3	$144.43	4.793%	$151.3525	$151.35	$151.35	$151.40
Purchase #4	$130.49	4.720%	$136.6491	$136.65	$136.65	$136.60
Purchase #5	$99.64	9.791%	$109.3958	$109.40	$109.40	$109.40
Purchase #6	$138.81	3.760%	$144.0293	$144.03	$144.05	$144.00
Purchase #7	$159.98	9.765%	$175.602	$175.60	$175.60	$175.60
7 purchase totals =	$920.53		$977.2293	$977.24	$977.25	$977.20