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	$118.85	10.494%	$131.3221	$131.32	$131.30	$131.30
Purchase #2	$98.35	13.286%	$111.4168	$111.42	$111.40	$111.40
Purchase #3	$49.56	10.439%	$54.7336	$54.73	$54.75	$54.70
Purchase #4	$106.60	4.426%	$111.3181	$111.32	$111.30	$111.30
Purchase #5	$12.69	6.135%	$13.4685	$13.47	$13.45	$13.50
Purchase #6	$222.95	9.161%	$243.3744	$243.37	$243.35	$243.40
Purchase #7	$181.26	13.818%	$206.3065	$206.31	$206.30	$206.30
7 purchase totals =	$790.26		$871.9400	$871.94	$871.85	$871.90