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	$38.69	3.302%	$39.9675	$39.97	$39.95	$40.00
Purchase #2	$130.90	12.665%	$147.4785	$147.48	$147.50	$147.50
Purchase #3	$32.52	4.342%	$33.932	$33.93	$33.95	$33.90
Purchase #4	$78.47	13.199%	$88.8273	$88.83	$88.85	$88.80
Purchase #5	$249.35	10.837%	$276.3721	$276.37	$276.35	$276.40
Purchase #6	$163.96	5.874%	$173.591	$173.59	$173.60	$173.60
Purchase #7	$119.33	10.331%	$131.658	$131.66	$131.65	$131.70
7 purchase totals =	$813.22		$891.8264	$891.83	$891.85	$891.90