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	$76.51	5.636%	$80.8221	$80.82	$80.80	$80.80
Purchase #2	$197.76	11.825%	$221.1451	$221.15	$221.15	$221.10
Purchase #3	$78.32	13.563%	$88.9425	$88.94	$88.95	$88.90
Purchase #4	$19.33	13.630%	$21.9647	$21.96	$21.95	$22.00
Purchase #5	$194.86	5.250%	$205.0902	$205.09	$205.10	$205.10
Purchase #6	$13.67	13.580%	$15.5264	$15.53	$15.55	$15.50
Purchase #7	$113.27	9.295%	$123.7984	$123.80	$123.80	$123.80
7 purchase totals =	$693.72		$757.2894	$757.29	$757.30	$757.20