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	$198.31	5.752%	$209.7168	$209.72	$209.70	$209.70
Purchase #2	$80.86	7.365%	$86.8153	$86.82	$86.80	$86.80
Purchase #3	$83.74	3.310%	$86.5118	$86.51	$86.50	$86.50
Purchase #4	$167.70	3.354%	$173.3247	$173.32	$173.30	$173.30
Purchase #5	$37.71	12.615%	$42.4671	$42.47	$42.45	$42.50
Purchase #6	$64.39	3.735%	$66.795	$66.80	$66.80	$66.80
Purchase #7	$126.41	5.336%	$133.1552	$133.16	$133.15	$133.20
7 purchase totals =	$759.12		$798.7859	$798.80	$798.70	$798.80