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	$142.52	12.490%	$160.3207	$160.32	$160.30	$160.30
Purchase #2	$73.73	10.672%	$81.5985	$81.60	$81.60	$81.60
Purchase #3	$168.30	12.585%	$189.4806	$189.48	$189.50	$189.50
Purchase #4	$222.52	5.822%	$235.4751	$235.48	$235.50	$235.50
Purchase #5	$172.46	6.493%	$183.6578	$183.66	$183.65	$183.70
Purchase #6	$221.56	8.518%	$240.4325	$240.43	$240.45	$240.40
Purchase #7	$70.89	8.380%	$76.8306	$76.83	$76.85	$76.80
7 purchase totals =	$1,071.98		$1,167.7958	$1,167.80	$1,167.85	$1,167.80