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	$76.31	12.559%	$85.8938	$85.89	$85.90	$85.90
Purchase #2	$153.54	4.135%	$159.8889	$159.89	$159.90	$159.90
Purchase #3	$174.82	11.562%	$195.0327	$195.03	$195.05	$195.00
Purchase #4	$137.69	11.460%	$153.4693	$153.47	$153.45	$153.50
Purchase #5	$20.69	5.126%	$21.7506	$21.75	$21.75	$21.80
Purchase #6	$193.57	11.748%	$216.3106	$216.31	$216.30	$216.30
Purchase #7	$94.96	3.808%	$98.5761	$98.58	$98.60	$98.60
7 purchase totals =	$851.58		$930.9220	$930.92	$930.95	$931.00