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	$90.37	5.766%	$95.5807	$95.58	$95.60	$95.60
Purchase #2	$78.95	8.830%	$85.9213	$85.92	$85.90	$85.90
Purchase #3	$97.64	7.259%	$104.7277	$104.73	$104.75	$104.70
Purchase #4	$57.29	9.488%	$62.7257	$62.73	$62.75	$62.70
Purchase #5	$140.85	8.268%	$152.4955	$152.50	$152.50	$152.50
Purchase #6	$101.98	6.748%	$108.8616	$108.86	$108.85	$108.90
Purchase #7	$55.66	5.572%	$58.7614	$58.76	$58.75	$58.80
7 purchase totals =	$622.74		$669.0739	$669.08	$669.10	$669.10