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	$206.43	8.458%	$223.8898	$223.89	$223.90	$223.90
Purchase #2	$168.96	8.625%	$183.5328	$183.53	$183.55	$183.50
Purchase #3	$173.98	3.424%	$179.9371	$179.94	$179.95	$179.90
Purchase #4	$196.38	13.140%	$222.1843	$222.18	$222.20	$222.20
Purchase #5	$193.48	7.860%	$208.6875	$208.69	$208.70	$208.70
Purchase #6	$19.56	11.139%	$21.7388	$21.74	$21.75	$21.70
Purchase #7	$207.89	5.281%	$218.8687	$218.87	$218.85	$218.90
7 purchase totals =	$1,166.68		$1,258.8390	$1,258.84	$1,258.90	$1,258.80