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	$129.78	13.856%	$147.7623	$147.76	$147.75	$147.80
Purchase #2	$197.50	13.219%	$223.6075	$223.61	$223.60	$223.60
Purchase #3	$64.43	10.366%	$71.1088	$71.11	$71.10	$71.10
Purchase #4	$58.42	13.814%	$66.4901	$66.49	$66.50	$66.50
Purchase #5	$229.56	8.723%	$249.5845	$249.58	$249.60	$249.60
Purchase #6	$42.99	6.182%	$45.6476	$45.65	$45.65	$45.60
Purchase #7	$175.87	11.775%	$196.5787	$196.58	$196.60	$196.60
7 purchase totals =	$898.55		$1,000.7795	$1,000.78	$1,000.80	$1,000.80