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	$51.51	3.112%	$53.113	$53.11	$53.10	$53.10
Purchase #2	$53.29	5.589%	$56.2684	$56.27	$56.25	$56.30
Purchase #3	$237.92	8.835%	$258.9402	$258.94	$258.95	$258.90
Purchase #4	$172.92	12.128%	$193.8917	$193.89	$193.90	$193.90
Purchase #5	$238.46	6.298%	$253.4782	$253.48	$253.50	$253.50
Purchase #6	$45.65	8.531%	$49.5444	$49.54	$49.55	$49.50
Purchase #7	$119.82	7.611%	$128.9395	$128.94	$128.95	$128.90
7 purchase totals =	$919.57		$994.1754	$994.17	$994.20	$994.10