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	$152.48	11.113%	$169.4251	$169.43	$169.45	$169.40
Purchase #2	$44.75	8.127%	$48.3868	$48.39	$48.40	$48.40
Purchase #3	$238.88	12.158%	$267.923	$267.92	$267.90	$267.90
Purchase #4	$207.90	11.191%	$231.1661	$231.17	$231.15	$231.20
Purchase #5	$29.54	5.622%	$31.2007	$31.20	$31.20	$31.20
Purchase #6	$87.73	3.521%	$90.819	$90.82	$90.80	$90.80
Purchase #7	$35.79	9.818%	$39.3039	$39.30	$39.30	$39.30
7 purchase totals =	$797.07		$878.2246	$878.23	$878.20	$878.20