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	$90.28	10.772%	$100.005	$100.01	$100.00	$100.00
Purchase #2	$81.69	4.476%	$85.3464	$85.35	$85.35	$85.30
Purchase #3	$79.83	11.150%	$88.731	$88.73	$88.75	$88.70
Purchase #4	$248.84	5.419%	$262.3246	$262.32	$262.30	$262.30
Purchase #5	$104.28	11.115%	$115.8707	$115.87	$115.85	$115.90
Purchase #6	$75.62	13.430%	$85.7758	$85.78	$85.80	$85.80
Purchase #7	$69.60	4.215%	$72.5336	$72.53	$72.55	$72.50
7 purchase totals =	$750.14		$810.5871	$810.59	$810.60	$810.50