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	$155.64	9.357%	$170.2032	$170.20	$170.20	$170.20
Purchase #2	$165.42	13.701%	$188.0842	$188.08	$188.10	$188.10
Purchase #3	$101.38	9.853%	$111.369	$111.37	$111.35	$111.40
Purchase #4	$197.47	10.185%	$217.5823	$217.58	$217.60	$217.60
Purchase #5	$104.34	7.464%	$112.1279	$112.13	$112.15	$112.10
Purchase #6	$220.80	6.861%	$235.9491	$235.95	$235.95	$235.90
Purchase #7	$109.51	5.544%	$115.5812	$115.58	$115.60	$115.60
7 purchase totals =	$1,054.56		$1,150.8969	$1,150.89	$1,150.95	$1,150.90