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	$45.65	10.168%	$50.2917	$50.29	$50.30	$50.30
Purchase #2	$28.31	4.703%	$29.6414	$29.64	$29.65	$29.60
Purchase #3	$196.48	9.849%	$215.8313	$215.83	$215.85	$215.80
Purchase #4	$237.74	11.212%	$264.3954	$264.40	$264.40	$264.40
Purchase #5	$141.83	7.495%	$152.4602	$152.46	$152.45	$152.50
Purchase #6	$75.32	13.227%	$85.2826	$85.28	$85.30	$85.30
Purchase #7	$61.25	9.363%	$66.9848	$66.98	$67.00	$67.00
7 purchase totals =	$786.58		$864.8874	$864.88	$864.95	$864.90