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	$69.27	13.178%	$78.3984	$78.40	$78.40	$78.40
Purchase #2	$48.73	5.485%	$51.4028	$51.40	$51.40	$51.40
Purchase #3	$139.37	3.230%	$143.8717	$143.87	$143.85	$143.90
Purchase #4	$186.58	6.365%	$198.4558	$198.46	$198.45	$198.50
Purchase #5	$157.86	9.783%	$173.3034	$173.30	$173.30	$173.30
Purchase #6	$221.85	7.471%	$238.4244	$238.42	$238.40	$238.40
Purchase #7	$169.33	7.740%	$182.4361	$182.44	$182.45	$182.40
7 purchase totals =	$992.99		$1,066.2926	$1,066.29	$1,066.25	$1,066.30