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	$154.41	8.405%	$167.3882	$167.39	$167.40	$167.40
Purchase #2	$38.93	5.628%	$41.121	$41.12	$41.10	$41.10
Purchase #3	$30.69	3.180%	$31.6659	$31.67	$31.65	$31.70
Purchase #4	$82.26	8.350%	$89.1287	$89.13	$89.15	$89.10
Purchase #5	$68.81	10.144%	$75.7901	$75.79	$75.80	$75.80
Purchase #6	$213.47	11.667%	$238.3755	$238.38	$238.40	$238.40
Purchase #7	$172.68	13.762%	$196.4442	$196.44	$196.45	$196.40
7 purchase totals =	$761.25		$839.9136	$839.92	$839.95	$839.90