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	$76.48	8.446%	$82.9395	$82.94	$82.95	$82.90
Purchase #2	$220.39	13.131%	$249.3294	$249.33	$249.35	$249.30
Purchase #3	$40.34	11.300%	$44.8984	$44.90	$44.90	$44.90
Purchase #4	$228.76	10.543%	$252.8782	$252.88	$252.90	$252.90
Purchase #5	$114.60	4.395%	$119.6367	$119.64	$119.65	$119.60
Purchase #6	$162.30	6.537%	$172.9096	$172.91	$172.90	$172.90
Purchase #7	$48.59	5.658%	$51.3392	$51.34	$51.35	$51.30
7 purchase totals =	$891.46		$973.9310	$973.94	$974.00	$973.80