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	$236.74	7.657%	$254.8672	$254.87	$254.85	$254.90
Purchase #2	$58.52	12.431%	$65.7946	$65.79	$65.80	$65.80
Purchase #3	$103.38	13.210%	$117.0365	$117.04	$117.05	$117.00
Purchase #4	$81.86	12.517%	$92.1064	$92.11	$92.10	$92.10
Purchase #5	$178.34	7.581%	$191.86	$191.86	$191.85	$191.90
Purchase #6	$49.43	7.492%	$53.1333	$53.13	$53.15	$53.10
Purchase #7	$85.93	4.844%	$90.0924	$90.09	$90.10	$90.10
7 purchase totals =	$794.20		$864.8904	$864.89	$864.90	$864.90