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	$225.69	13.119%	$255.2983	$255.30	$255.30	$255.30
Purchase #2	$235.54	9.631%	$258.2249	$258.22	$258.20	$258.20
Purchase #3	$210.46	6.624%	$224.4009	$224.40	$224.40	$224.40
Purchase #4	$161.82	4.120%	$168.487	$168.49	$168.50	$168.50
Purchase #5	$99.52	9.551%	$109.0252	$109.03	$109.05	$109.00
Purchase #6	$53.73	11.865%	$60.1051	$60.11	$60.10	$60.10
Purchase #7	$149.93	11.691%	$167.4583	$167.46	$167.45	$167.50
7 purchase totals =	$1,136.69		$1,242.9997	$1,243.01	$1,243.00	$1,243.00