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	$248.41	12.171%	$278.644	$278.64	$278.65	$278.60
Purchase #2	$174.87	12.237%	$196.2688	$196.27	$196.25	$196.30
Purchase #3	$77.44	4.763%	$81.1285	$81.13	$81.15	$81.10
Purchase #4	$79.82	13.658%	$90.7218	$90.72	$90.70	$90.70
Purchase #5	$202.88	6.872%	$216.8219	$216.82	$216.80	$216.80
Purchase #6	$180.68	5.454%	$190.5343	$190.53	$190.55	$190.50
Purchase #7	$230.36	6.382%	$245.0616	$245.06	$245.05	$245.10
7 purchase totals =	$1,194.46		$1,299.1809	$1,299.17	$1,299.15	$1,299.10