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	$162.91	9.623%	$178.5868	$178.59	$178.60	$178.60
Purchase #2	$84.82	7.781%	$91.4198	$91.42	$91.40	$91.40
Purchase #3	$5.84	11.415%	$6.5066	$6.51	$6.50	$6.50
Purchase #4	$83.55	8.386%	$90.5565	$90.56	$90.55	$90.60
Purchase #5	$26.27	7.189%	$28.1586	$28.16	$28.15	$28.20
Purchase #6	$127.77	4.440%	$133.443	$133.44	$133.45	$133.40
Purchase #7	$145.62	3.647%	$150.9308	$150.93	$150.95	$150.90
7 purchase totals =	$636.78		$679.6021	$679.61	$679.60	$679.60