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	$110.73	10.708%	$122.587	$122.59	$122.60	$122.60
Purchase #2	$233.88	13.174%	$264.6914	$264.69	$264.70	$264.70
Purchase #3	$110.46	8.453%	$119.7972	$119.80	$119.80	$119.80
Purchase #4	$213.70	5.129%	$224.6607	$224.66	$224.65	$224.70
Purchase #5	$78.71	5.359%	$82.9281	$82.93	$82.95	$82.90
Purchase #6	$49.73	11.766%	$55.5812	$55.58	$55.60	$55.60
Purchase #7	$107.49	3.713%	$111.4811	$111.48	$111.50	$111.50
7 purchase totals =	$904.70		$981.7267	$981.73	$981.80	$981.80