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	$97.53	3.479%	$100.9231	$100.92	$100.90	$100.90
Purchase #2	$40.26	6.868%	$43.0251	$43.03	$43.05	$43.00
Purchase #3	$104.94	6.498%	$111.759	$111.76	$111.75	$111.80
Purchase #4	$29.99	8.716%	$32.6039	$32.60	$32.60	$32.60
Purchase #5	$35.39	12.289%	$39.7391	$39.74	$39.75	$39.70
Purchase #6	$177.29	12.282%	$199.0648	$199.06	$199.05	$199.10
Purchase #7	$129.28	9.337%	$141.3509	$141.35	$141.35	$141.40
7 purchase totals =	$614.68		$668.4659	$668.46	$668.45	$668.50