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	$92.58	13.254%	$104.8506	$104.85	$104.85	$104.90
Purchase #2	$234.60	13.688%	$266.712	$266.71	$266.70	$266.70
Purchase #3	$129.47	3.152%	$133.5509	$133.55	$133.55	$133.60
Purchase #4	$84.30	6.245%	$89.5645	$89.56	$89.55	$89.60
Purchase #5	$147.54	7.713%	$158.9198	$158.92	$158.90	$158.90
Purchase #6	$19.58	6.168%	$20.7877	$20.79	$20.80	$20.80
Purchase #7	$47.71	3.860%	$49.5516	$49.55	$49.55	$49.60
7 purchase totals =	$755.78		$823.9371	$823.93	$823.90	$824.10