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	$134.74	5.740%	$142.4741	$142.47	$142.45	$142.50
Purchase #2	$68.70	13.773%	$78.1621	$78.16	$78.15	$78.20
Purchase #3	$67.45	13.771%	$76.7385	$76.74	$76.75	$76.70
Purchase #4	$53.83	3.717%	$55.8309	$55.83	$55.85	$55.80
Purchase #5	$17.40	8.757%	$18.9237	$18.92	$18.90	$18.90
Purchase #6	$186.42	4.787%	$195.3439	$195.34	$195.35	$195.30
Purchase #7	$240.25	6.195%	$255.1335	$255.13	$255.15	$255.10
7 purchase totals =	$768.79		$822.6067	$822.59	$822.60	$822.50