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	$37.43	12.476%	$42.0998	$42.10	$42.10	$42.10
Purchase #2	$78.78	13.798%	$89.6501	$89.65	$89.65	$89.70
Purchase #3	$129.46	6.102%	$137.3596	$137.36	$137.35	$137.40
Purchase #4	$198.97	4.615%	$208.1525	$208.15	$208.15	$208.20
Purchase #5	$148.68	6.433%	$158.2446	$158.24	$158.25	$158.20
Purchase #6	$68.85	3.359%	$71.1627	$71.16	$71.15	$71.20
Purchase #7	$225.56	10.606%	$249.4829	$249.48	$249.50	$249.50
7 purchase totals =	$887.73		$956.1522	$956.14	$956.15	$956.30