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	$67.97	3.865%	$70.597	$70.60	$70.60	$70.60
Purchase #2	$215.89	4.839%	$226.3369	$226.34	$226.35	$226.30
Purchase #3	$99.65	12.839%	$112.4441	$112.44	$112.45	$112.40
Purchase #4	$53.94	13.637%	$61.2958	$61.30	$61.30	$61.30
Purchase #5	$15.40	12.301%	$17.2944	$17.29	$17.30	$17.30
Purchase #6	$40.71	3.752%	$42.2374	$42.24	$42.25	$42.20
Purchase #7	$56.58	11.818%	$63.2666	$63.27	$63.25	$63.30
7 purchase totals =	$550.14		$593.4722	$593.48	$593.50	$593.40