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	$102.81	6.507%	$109.4998	$109.50	$109.50	$109.50
Purchase #2	$138.85	8.822%	$151.0993	$151.10	$151.10	$151.10
Purchase #3	$109.62	12.739%	$123.5845	$123.58	$123.60	$123.60
Purchase #4	$111.41	4.643%	$116.5828	$116.58	$116.60	$116.60
Purchase #5	$98.64	3.241%	$101.8369	$101.84	$101.85	$101.80
Purchase #6	$82.39	4.287%	$85.9221	$85.92	$85.90	$85.90
Purchase #7	$211.55	9.749%	$232.174	$232.17	$232.15	$232.20
7 purchase totals =	$855.27		$920.6994	$920.69	$920.70	$920.70