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	$56.74	5.618%	$59.9277	$59.93	$59.95	$59.90
Purchase #2	$208.61	10.641%	$230.8082	$230.81	$230.80	$230.80
Purchase #3	$178.57	8.791%	$194.2681	$194.27	$194.25	$194.30
Purchase #4	$50.46	10.209%	$55.6115	$55.61	$55.60	$55.60
Purchase #5	$143.38	13.327%	$162.4883	$162.49	$162.50	$162.50
Purchase #6	$72.47	10.134%	$79.8141	$79.81	$79.80	$79.80
Purchase #7	$49.46	10.192%	$54.501	$54.50	$54.50	$54.50
7 purchase totals =	$759.69		$837.4189	$837.42	$837.40	$837.40