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	$91.92	8.339%	$99.5852	$99.59	$99.60	$99.60
Purchase #2	$149.33	12.718%	$168.3218	$168.32	$168.30	$168.30
Purchase #3	$185.45	6.124%	$196.807	$196.81	$196.80	$196.80
Purchase #4	$63.64	4.854%	$66.7291	$66.73	$66.75	$66.70
Purchase #5	$124.89	11.526%	$139.2848	$139.28	$139.30	$139.30
Purchase #6	$13.87	13.577%	$15.7531	$15.75	$15.75	$15.80
Purchase #7	$36.86	12.113%	$41.3249	$41.32	$41.30	$41.30
7 purchase totals =	$665.96		$727.8059	$727.80	$727.80	$727.80