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	$119.91	8.166%	$129.7019	$129.70	$129.70	$129.70
Purchase #2	$36.30	5.548%	$38.3139	$38.31	$38.30	$38.30
Purchase #3	$204.61	7.141%	$219.2212	$219.22	$219.20	$219.20
Purchase #4	$190.94	9.419%	$208.9246	$208.92	$208.90	$208.90
Purchase #5	$153.27	9.542%	$167.895	$167.90	$167.90	$167.90
Purchase #6	$146.34	12.109%	$164.0603	$164.06	$164.05	$164.10
Purchase #7	$40.85	10.761%	$45.2459	$45.25	$45.25	$45.20
7 purchase totals =	$892.22		$973.3628	$973.36	$973.30	$973.30