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	$134.73	5.473%	$142.1038	$142.10	$142.10	$142.10
Purchase #2	$105.38	13.799%	$119.9214	$119.92	$119.90	$119.90
Purchase #3	$145.75	9.872%	$160.1384	$160.14	$160.15	$160.10
Purchase #4	$102.94	4.318%	$107.3849	$107.38	$107.40	$107.40
Purchase #5	$244.42	4.385%	$255.1378	$255.14	$255.15	$255.10
Purchase #6	$18.79	13.469%	$21.3208	$21.32	$21.30	$21.30
Purchase #7	$23.94	10.676%	$26.4958	$26.50	$26.50	$26.50
7 purchase totals =	$775.95		$832.5029	$832.50	$832.50	$832.40