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	$12.62	3.716%	$13.089	$13.09	$13.10	$13.10
Purchase #2	$59.60	11.157%	$66.2496	$66.25	$66.25	$66.20
Purchase #3	$61.43	10.543%	$67.9066	$67.91	$67.90	$67.90
Purchase #4	$202.94	13.154%	$229.6347	$229.63	$229.65	$229.60
Purchase #5	$94.88	3.420%	$98.1249	$98.12	$98.10	$98.10
Purchase #6	$19.60	8.742%	$21.3134	$21.31	$21.30	$21.30
Purchase #7	$19.55	11.871%	$21.8708	$21.87	$21.85	$21.90
7 purchase totals =	$470.62		$518.1890	$518.18	$518.15	$518.10