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	$154.62	3.763%	$160.4384	$160.44	$160.45	$160.40
Purchase #2	$39.54	13.191%	$44.7557	$44.76	$44.75	$44.80
Purchase #3	$64.95	11.861%	$72.6537	$72.65	$72.65	$72.70
Purchase #4	$127.41	12.406%	$143.2165	$143.22	$143.20	$143.20
Purchase #5	$207.47	10.802%	$229.8809	$229.88	$229.90	$229.90
Purchase #6	$105.33	7.160%	$112.8716	$112.87	$112.85	$112.90
Purchase #7	$72.55	13.317%	$82.2115	$82.21	$82.20	$82.20
7 purchase totals =	$771.87		$846.0283	$846.03	$846.00	$846.10