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	$85.81	4.328%	$89.5239	$89.52	$89.50	$89.50
Purchase #2	$125.45	4.140%	$130.6436	$130.64	$130.65	$130.60
Purchase #3	$78.44	4.849%	$82.2436	$82.24	$82.25	$82.20
Purchase #4	$102.30	5.682%	$108.1127	$108.11	$108.10	$108.10
Purchase #5	$151.78	4.313%	$158.3263	$158.33	$158.35	$158.30
Purchase #6	$246.38	5.772%	$260.6011	$260.60	$260.60	$260.60
Purchase #7	$232.59	9.120%	$253.8022	$253.80	$253.80	$253.80
7 purchase totals =	$1,022.75		$1,083.2534	$1,083.24	$1,083.25	$1,083.10