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	$150.92	13.464%	$171.2399	$171.24	$171.25	$171.20
Purchase #2	$165.89	5.696%	$175.3391	$175.34	$175.35	$175.30
Purchase #3	$163.76	13.245%	$185.45	$185.45	$185.45	$185.50
Purchase #4	$30.39	6.838%	$32.4681	$32.47	$32.45	$32.50
Purchase #5	$16.76	10.162%	$18.4632	$18.46	$18.45	$18.50
Purchase #6	$123.60	8.669%	$134.3149	$134.31	$134.30	$134.30
Purchase #7	$37.42	7.328%	$40.1621	$40.16	$40.15	$40.20
7 purchase totals =	$688.74		$757.4373	$757.43	$757.40	$757.50