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	$185.74	5.748%	$196.4163	$196.42	$196.40	$196.40
Purchase #2	$114.40	7.868%	$123.401	$123.40	$123.40	$123.40
Purchase #3	$20.45	13.591%	$23.2294	$23.23	$23.25	$23.20
Purchase #4	$61.46	13.167%	$69.5524	$69.55	$69.55	$69.60
Purchase #5	$211.93	12.836%	$239.1333	$239.13	$239.15	$239.10
Purchase #6	$70.42	12.162%	$78.9845	$78.98	$79.00	$79.00
Purchase #7	$30.30	9.440%	$33.1603	$33.16	$33.15	$33.20
7 purchase totals =	$694.70		$763.8772	$763.87	$763.90	$763.90