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	$16.44	11.705%	$18.3643	$18.36	$18.35	$18.40
Purchase #2	$78.96	11.788%	$88.2678	$88.27	$88.25	$88.30
Purchase #3	$165.57	4.330%	$172.7392	$172.74	$172.75	$172.70
Purchase #4	$214.62	3.191%	$221.4685	$221.47	$221.45	$221.50
Purchase #5	$55.97	11.796%	$62.5722	$62.57	$62.55	$62.60
Purchase #6	$222.75	12.497%	$250.5871	$250.59	$250.60	$250.60
Purchase #7	$154.46	8.123%	$167.0068	$167.01	$167.00	$167.00
7 purchase totals =	$908.77		$981.0059	$981.01	$980.95	$981.10