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	$74.42	12.248%	$83.535	$83.54	$83.55	$83.50
Purchase #2	$79.36	7.848%	$85.5882	$85.59	$85.60	$85.60
Purchase #3	$134.69	4.303%	$140.4857	$140.49	$140.50	$140.50
Purchase #4	$42.75	6.479%	$45.5198	$45.52	$45.50	$45.50
Purchase #5	$76.53	5.762%	$80.9397	$80.94	$80.95	$80.90
Purchase #6	$32.51	5.275%	$34.2249	$34.22	$34.20	$34.20
Purchase #7	$202.91	13.813%	$230.938	$230.94	$230.95	$230.90
7 purchase totals =	$643.17		$701.2313	$701.24	$701.25	$701.10