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	$67.36	6.102%	$71.4703	$71.47	$71.45	$71.50
Purchase #2	$39.50	7.856%	$42.6031	$42.60	$42.60	$42.60
Purchase #3	$180.84	8.566%	$196.3308	$196.33	$196.35	$196.30
Purchase #4	$167.83	4.746%	$175.7952	$175.80	$175.80	$175.80
Purchase #5	$82.78	9.546%	$90.6822	$90.68	$90.70	$90.70
Purchase #6	$153.85	13.830%	$175.1275	$175.13	$175.15	$175.10
Purchase #7	$53.78	12.269%	$60.3783	$60.38	$60.40	$60.40
7 purchase totals =	$745.94		$812.3874	$812.39	$812.45	$812.40