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	$185.27	13.163%	$209.6571	$209.66	$209.65	$209.70
Purchase #2	$40.46	4.734%	$42.3754	$42.38	$42.40	$42.40
Purchase #3	$56.42	12.277%	$63.3467	$63.35	$63.35	$63.30
Purchase #4	$223.80	11.613%	$249.7899	$249.79	$249.80	$249.80
Purchase #5	$208.72	6.314%	$221.8986	$221.90	$221.90	$221.90
Purchase #6	$106.88	13.410%	$121.2126	$121.21	$121.20	$121.20
Purchase #7	$38.92	8.347%	$42.1687	$42.17	$42.15	$42.20
7 purchase totals =	$860.47		$950.4490	$950.46	$950.45	$950.50