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	$127.38	12.860%	$143.7611	$143.76	$143.75	$143.80
Purchase #2	$241.76	7.474%	$259.8291	$259.83	$259.85	$259.80
Purchase #3	$98.62	13.171%	$111.6092	$111.61	$111.60	$111.60
Purchase #4	$91.61	12.423%	$102.9907	$102.99	$103.00	$103.00
Purchase #5	$58.61	9.512%	$64.185	$64.19	$64.20	$64.20
Purchase #6	$123.72	11.159%	$137.5259	$137.53	$137.55	$137.50
Purchase #7	$11.57	11.661%	$12.9192	$12.92	$12.90	$12.90
7 purchase totals =	$753.27		$832.8202	$832.83	$832.85	$832.80