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	$186.40	5.600%	$196.8384	$196.84	$196.85	$196.80
Purchase #2	$243.31	3.802%	$252.5606	$252.56	$252.55	$252.60
Purchase #3	$73.54	13.722%	$83.6312	$83.63	$83.65	$83.60
Purchase #4	$65.44	6.348%	$69.5941	$69.59	$69.60	$69.60
Purchase #5	$88.85	3.848%	$92.2689	$92.27	$92.25	$92.30
Purchase #6	$226.57	12.613%	$255.1473	$255.15	$255.15	$255.10
Purchase #7	$27.32	3.288%	$28.2183	$28.22	$28.20	$28.20
7 purchase totals =	$911.43		$978.2588	$978.26	$978.25	$978.20