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	$25.49	8.619%	$27.687	$27.69	$27.70	$27.70
Purchase #2	$130.46	8.710%	$141.8231	$141.82	$141.80	$141.80
Purchase #3	$166.34	13.300%	$188.4632	$188.46	$188.45	$188.50
Purchase #4	$173.95	12.810%	$196.233	$196.23	$196.25	$196.20
Purchase #5	$224.91	4.853%	$235.8249	$235.82	$235.80	$235.80
Purchase #6	$12.86	12.624%	$14.4834	$14.48	$14.50	$14.50
Purchase #7	$148.65	3.188%	$153.389	$153.39	$153.40	$153.40
7 purchase totals =	$882.66		$957.9036	$957.89	$957.90	$957.90