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	$240.45	13.700%	$273.3917	$273.39	$273.40	$273.40
Purchase #2	$223.65	6.509%	$238.2074	$238.21	$238.20	$238.20
Purchase #3	$83.70	13.636%	$95.1133	$95.11	$95.10	$95.10
Purchase #4	$184.46	11.275%	$205.2579	$205.26	$205.25	$205.30
Purchase #5	$66.80	8.866%	$72.7225	$72.72	$72.70	$72.70
Purchase #6	$110.93	6.212%	$117.821	$117.82	$117.80	$117.80
Purchase #7	$50.87	8.252%	$55.0678	$55.07	$55.05	$55.10
7 purchase totals =	$960.86		$1,057.5816	$1,057.58	$1,057.50	$1,057.60