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	$136.60	11.174%	$151.8637	$151.86	$151.85	$151.90
Purchase #2	$31.71	9.191%	$34.6245	$34.62	$34.60	$34.60
Purchase #3	$70.84	13.692%	$80.5394	$80.54	$80.55	$80.50
Purchase #4	$229.55	4.640%	$240.2011	$240.20	$240.20	$240.20
Purchase #5	$76.59	13.425%	$86.8722	$86.87	$86.85	$86.90
Purchase #6	$110.87	11.713%	$123.8562	$123.86	$123.85	$123.90
Purchase #7	$127.67	6.678%	$136.1958	$136.20	$136.20	$136.20
7 purchase totals =	$783.83		$854.1529	$854.15	$854.10	$854.20