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	$21.40	9.672%	$23.4698	$23.47	$23.45	$23.50
Purchase #2	$223.47	5.282%	$235.2737	$235.27	$235.25	$235.30
Purchase #3	$116.89	5.263%	$123.0419	$123.04	$123.05	$123.00
Purchase #4	$24.36	3.111%	$25.1178	$25.12	$25.10	$25.10
Purchase #5	$236.70	6.690%	$252.5352	$252.54	$252.55	$252.50
Purchase #6	$56.72	5.609%	$59.9014	$59.90	$59.90	$59.90
Purchase #7	$153.39	9.237%	$167.5586	$167.56	$167.55	$167.60
7 purchase totals =	$832.93		$886.8984	$886.90	$886.85	$886.90