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	$156.90	11.691%	$175.2432	$175.24	$175.25	$175.20
Purchase #2	$61.42	10.374%	$67.7917	$67.79	$67.80	$67.80
Purchase #3	$230.31	3.525%	$238.4284	$238.43	$238.45	$238.40
Purchase #4	$54.55	10.655%	$60.3623	$60.36	$60.35	$60.40
Purchase #5	$237.37	7.597%	$255.403	$255.40	$255.40	$255.40
Purchase #6	$13.69	10.781%	$15.1659	$15.17	$15.15	$15.20
Purchase #7	$137.49	13.567%	$156.1433	$156.14	$156.15	$156.10
7 purchase totals =	$891.73		$968.5378	$968.53	$968.55	$968.50