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	$249.36	11.227%	$277.3556	$277.36	$277.35	$277.40
Purchase #2	$83.30	11.372%	$92.7729	$92.77	$92.75	$92.80
Purchase #3	$80.80	11.744%	$90.2892	$90.29	$90.30	$90.30
Purchase #4	$247.39	11.386%	$275.5578	$275.56	$275.55	$275.60
Purchase #5	$249.42	7.637%	$268.4682	$268.47	$268.45	$268.50
Purchase #6	$94.60	6.665%	$100.9051	$100.91	$100.90	$100.90
Purchase #7	$75.77	10.332%	$83.5986	$83.60	$83.60	$83.60
7 purchase totals =	$1,080.64		$1,188.9474	$1,188.96	$1,188.90	$1,189.10