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	$11.30	12.414%	$12.7028	$12.70	$12.70	$12.70
Purchase #2	$55.64	13.855%	$63.3489	$63.35	$63.35	$63.30
Purchase #3	$159.25	3.511%	$164.8413	$164.84	$164.85	$164.80
Purchase #4	$229.84	13.264%	$260.326	$260.33	$260.35	$260.30
Purchase #5	$234.86	8.845%	$255.6334	$255.63	$255.65	$255.60
Purchase #6	$123.64	3.445%	$127.8994	$127.90	$127.90	$127.90
Purchase #7	$59.60	3.697%	$61.8034	$61.80	$61.80	$61.80
7 purchase totals =	$874.13		$946.5552	$946.55	$946.60	$946.40