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	$159.32	4.583%	$166.6216	$166.62	$166.60	$166.60
Purchase #2	$39.78	5.151%	$41.8291	$41.83	$41.85	$41.80
Purchase #3	$30.29	11.654%	$33.82	$33.82	$33.80	$33.80
Purchase #4	$213.37	3.869%	$221.6253	$221.63	$221.65	$221.60
Purchase #5	$12.57	12.627%	$14.1572	$14.16	$14.15	$14.20
Purchase #6	$153.35	13.630%	$174.2516	$174.25	$174.25	$174.30
Purchase #7	$28.46	3.568%	$29.4755	$29.48	$29.50	$29.50
7 purchase totals =	$637.14		$681.7803	$681.79	$681.80	$681.80