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	$49.81	11.185%	$55.3812	$55.38	$55.40	$55.40
Purchase #2	$88.30	13.807%	$100.4916	$100.49	$100.50	$100.50
Purchase #3	$106.47	10.697%	$117.8591	$117.86	$117.85	$117.90
Purchase #4	$56.94	13.247%	$64.4828	$64.48	$64.50	$64.50
Purchase #5	$68.47	10.570%	$75.7073	$75.71	$75.70	$75.70
Purchase #6	$91.36	11.729%	$102.0756	$102.08	$102.10	$102.10
Purchase #7	$5.72	12.860%	$6.4556	$6.46	$6.45	$6.50
7 purchase totals =	$467.07		$522.4532	$522.46	$522.50	$522.60