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	$82.65	6.526%	$88.0437	$88.04	$88.05	$88.00
Purchase #2	$99.55	7.360%	$106.8769	$106.88	$106.90	$106.90
Purchase #3	$112.57	5.353%	$118.5959	$118.60	$118.60	$118.60
Purchase #4	$164.75	13.412%	$186.8463	$186.85	$186.85	$186.80
Purchase #5	$53.92	9.653%	$59.1249	$59.12	$59.10	$59.10
Purchase #6	$221.69	8.485%	$240.5004	$240.50	$240.50	$240.50
Purchase #7	$84.91	4.318%	$88.5764	$88.58	$88.60	$88.60
7 purchase totals =	$820.04		$888.5645	$888.57	$888.60	$888.50