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	$57.77	3.200%	$59.6186	$59.62	$59.60	$59.60
Purchase #2	$156.80	13.728%	$178.3255	$178.33	$178.35	$178.30
Purchase #3	$82.97	8.358%	$89.9046	$89.90	$89.90	$89.90
Purchase #4	$90.32	13.638%	$102.6378	$102.64	$102.65	$102.60
Purchase #5	$103.90	8.728%	$112.9684	$112.97	$112.95	$113.00
Purchase #6	$157.74	7.680%	$169.8544	$169.85	$169.85	$169.90
Purchase #7	$174.28	12.621%	$196.2759	$196.28	$196.30	$196.30
7 purchase totals =	$823.78		$909.5852	$909.59	$909.60	$909.60