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	$170.53	8.421%	$184.8903	$184.89	$184.90	$184.90
Purchase #2	$83.36	8.167%	$90.168	$90.17	$90.15	$90.20
Purchase #3	$114.76	12.869%	$129.5285	$129.53	$129.55	$129.50
Purchase #4	$140.96	8.731%	$153.2672	$153.27	$153.25	$153.30
Purchase #5	$53.79	9.840%	$59.0829	$59.08	$59.10	$59.10
Purchase #6	$182.45	6.137%	$193.647	$193.65	$193.65	$193.60
Purchase #7	$182.60	3.825%	$189.5845	$189.58	$189.60	$189.60
7 purchase totals =	$928.45		$1,000.1684	$1,000.17	$1,000.20	$1,000.20