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	$52.80	6.724%	$56.3503	$56.35	$56.35	$56.40
Purchase #2	$212.69	13.335%	$241.0522	$241.05	$241.05	$241.10
Purchase #3	$78.30	10.194%	$86.2819	$86.28	$86.30	$86.30
Purchase #4	$236.48	5.458%	$249.3871	$249.39	$249.40	$249.40
Purchase #5	$80.91	10.672%	$89.5447	$89.54	$89.55	$89.50
Purchase #6	$11.97	6.668%	$12.7682	$12.77	$12.75	$12.80
Purchase #7	$38.42	10.199%	$42.3385	$42.34	$42.35	$42.30
7 purchase totals =	$711.57		$777.7229	$777.72	$777.75	$777.80