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	$50.43	9.656%	$55.2995	$55.30	$55.30	$55.30
Purchase #2	$205.88	5.269%	$216.7278	$216.73	$216.75	$216.70
Purchase #3	$189.77	3.433%	$196.2848	$196.28	$196.30	$196.30
Purchase #4	$85.94	5.127%	$90.3461	$90.35	$90.35	$90.30
Purchase #5	$17.94	11.667%	$20.0331	$20.03	$20.05	$20.00
Purchase #6	$239.49	3.871%	$248.7607	$248.76	$248.75	$248.80
Purchase #7	$16.52	12.461%	$18.5786	$18.58	$18.60	$18.60
7 purchase totals =	$805.97		$846.0306	$846.03	$846.10	$846.00