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	$31.80	9.396%	$34.7879	$34.79	$34.80	$34.80
Purchase #2	$130.83	12.572%	$147.2779	$147.28	$147.30	$147.30
Purchase #3	$178.37	10.810%	$197.6518	$197.65	$197.65	$197.70
Purchase #4	$120.72	5.669%	$127.5636	$127.56	$127.55	$127.60
Purchase #5	$141.54	7.687%	$152.4202	$152.42	$152.40	$152.40
Purchase #6	$108.92	13.505%	$123.6296	$123.63	$123.65	$123.60
Purchase #7	$79.94	12.348%	$89.811	$89.81	$89.80	$89.80
7 purchase totals =	$792.12		$873.1420	$873.14	$873.15	$873.20