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	$149.39	11.376%	$166.3846	$166.38	$166.40	$166.40
Purchase #2	$31.46	7.598%	$33.8503	$33.85	$33.85	$33.90
Purchase #3	$104.31	10.397%	$115.1551	$115.16	$115.15	$115.20
Purchase #4	$167.42	3.299%	$172.9432	$172.94	$172.95	$172.90
Purchase #5	$196.91	12.561%	$221.6439	$221.64	$221.65	$221.60
Purchase #6	$49.45	6.810%	$52.8175	$52.82	$52.80	$52.80
Purchase #7	$20.53	8.103%	$22.1935	$22.19	$22.20	$22.20
7 purchase totals =	$719.47		$784.9881	$784.98	$785.00	$785.00