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	$85.26	4.790%	$89.344	$89.34	$89.35	$89.30
Purchase #2	$28.51	8.524%	$30.9402	$30.94	$30.95	$30.90
Purchase #3	$80.85	3.826%	$83.9433	$83.94	$83.95	$83.90
Purchase #4	$53.71	10.634%	$59.4215	$59.42	$59.40	$59.40
Purchase #5	$65.84	3.233%	$67.9686	$67.97	$67.95	$68.00
Purchase #6	$234.45	12.867%	$264.6167	$264.62	$264.60	$264.60
Purchase #7	$30.60	8.766%	$33.2824	$33.28	$33.30	$33.30
7 purchase totals =	$579.22		$629.5167	$629.51	$629.50	$629.40