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	$53.87	12.155%	$60.4179	$60.42	$60.40	$60.40
Purchase #2	$37.56	10.328%	$41.4392	$41.44	$41.45	$41.40
Purchase #3	$67.27	13.511%	$76.3588	$76.36	$76.35	$76.40
Purchase #4	$134.62	11.622%	$150.2655	$150.27	$150.25	$150.30
Purchase #5	$203.96	11.103%	$226.6057	$226.61	$226.60	$226.60
Purchase #6	$89.56	11.351%	$99.726	$99.73	$99.75	$99.70
Purchase #7	$11.44	6.699%	$12.2064	$12.21	$12.20	$12.20
7 purchase totals =	$598.28		$667.0195	$667.04	$667.00	$667.00