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	$126.86	8.557%	$137.7154	$137.72	$137.70	$137.70
Purchase #2	$199.25	7.629%	$214.4508	$214.45	$214.45	$214.50
Purchase #3	$52.95	5.303%	$55.7579	$55.76	$55.75	$55.80
Purchase #4	$119.34	3.844%	$123.9274	$123.93	$123.95	$123.90
Purchase #5	$117.33	8.351%	$127.1282	$127.13	$127.15	$127.10
Purchase #6	$65.76	3.232%	$67.8854	$67.89	$67.90	$67.90
Purchase #7	$79.61	10.687%	$88.1179	$88.12	$88.10	$88.10
7 purchase totals =	$761.10		$814.9830	$815.00	$815.00	$815.00