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	$187.67	12.687%	$211.4797	$211.48	$211.50	$211.50
Purchase #2	$239.64	6.506%	$255.231	$255.23	$255.25	$255.20
Purchase #3	$141.43	13.147%	$160.0238	$160.02	$160.00	$160.00
Purchase #4	$103.51	5.573%	$109.2786	$109.28	$109.30	$109.30
Purchase #5	$104.28	12.555%	$117.3724	$117.37	$117.35	$117.40
Purchase #6	$162.74	13.757%	$185.1281	$185.13	$185.15	$185.10
Purchase #7	$36.92	5.127%	$38.8129	$38.81	$38.80	$38.80
7 purchase totals =	$976.19		$1,077.3265	$1,077.32	$1,077.35	$1,077.30