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	$85.74	5.662%	$90.5946	$90.59	$90.60	$90.60
Purchase #2	$200.68	7.780%	$216.2929	$216.29	$216.30	$216.30
Purchase #3	$210.98	7.464%	$226.7275	$226.73	$226.75	$226.70
Purchase #4	$177.44	5.318%	$186.8763	$186.88	$186.90	$186.90
Purchase #5	$27.58	3.221%	$28.4684	$28.47	$28.45	$28.50
Purchase #6	$53.78	9.836%	$59.0698	$59.07	$59.05	$59.10
Purchase #7	$10.93	11.505%	$12.1875	$12.19	$12.20	$12.20
7 purchase totals =	$767.13		$820.2170	$820.22	$820.25	$820.30