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	$5.94	8.539%	$6.4472	$6.45	$6.45	$6.40
Purchase #2	$158.26	9.215%	$172.8437	$172.84	$172.85	$172.80
Purchase #3	$75.37	9.792%	$82.7502	$82.75	$82.75	$82.80
Purchase #4	$78.45	9.577%	$85.9632	$85.96	$85.95	$86.00
Purchase #5	$160.83	7.588%	$173.0338	$173.03	$173.05	$173.00
Purchase #6	$203.45	5.847%	$215.3457	$215.35	$215.35	$215.30
Purchase #7	$204.42	10.190%	$225.2504	$225.25	$225.25	$225.30
7 purchase totals =	$886.72		$961.6342	$961.63	$961.65	$961.60