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	$41.90	3.126%	$43.2098	$43.21	$43.20	$43.20
Purchase #2	$164.87	10.483%	$182.1533	$182.15	$182.15	$182.20
Purchase #3	$82.39	11.174%	$91.5963	$91.60	$91.60	$91.60
Purchase #4	$33.74	7.228%	$36.1787	$36.18	$36.20	$36.20
Purchase #5	$156.72	5.865%	$165.9116	$165.91	$165.90	$165.90
Purchase #6	$31.69	9.833%	$34.8061	$34.81	$34.80	$34.80
Purchase #7	$45.59	6.383%	$48.5	$48.50	$48.50	$48.50
7 purchase totals =	$556.90		$602.3558	$602.36	$602.35	$602.40