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	$115.74	12.429%	$130.1253	$130.13	$130.15	$130.10
Purchase #2	$151.53	9.628%	$166.1193	$166.12	$166.10	$166.10
Purchase #3	$96.44	4.102%	$100.396	$100.40	$100.40	$100.40
Purchase #4	$40.55	4.466%	$42.361	$42.36	$42.35	$42.40
Purchase #5	$205.37	6.182%	$218.066	$218.07	$218.05	$218.10
Purchase #6	$108.72	13.501%	$123.3983	$123.40	$123.40	$123.40
Purchase #7	$195.54	6.863%	$208.9599	$208.96	$208.95	$209.00
7 purchase totals =	$913.89		$989.4258	$989.44	$989.40	$989.50