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	$213.31	4.718%	$223.374	$223.37	$223.35	$223.40
Purchase #2	$91.52	10.739%	$101.3483	$101.35	$101.35	$101.30
Purchase #3	$41.52	3.170%	$42.8362	$42.84	$42.85	$42.80
Purchase #4	$72.46	3.699%	$75.1403	$75.14	$75.15	$75.10
Purchase #5	$122.92	13.401%	$139.3925	$139.39	$139.40	$139.40
Purchase #6	$112.97	10.150%	$124.4365	$124.44	$124.45	$124.40
Purchase #7	$247.86	10.405%	$273.6498	$273.65	$273.65	$273.60
7 purchase totals =	$902.56		$980.1776	$980.18	$980.20	$980.00