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	$29.97	3.722%	$31.0855	$31.09	$31.10	$31.10
Purchase #2	$247.58	8.608%	$268.8917	$268.89	$268.90	$268.90
Purchase #3	$125.48	10.863%	$139.1109	$139.11	$139.10	$139.10
Purchase #4	$215.60	6.376%	$229.3467	$229.35	$229.35	$229.30
Purchase #5	$118.28	4.433%	$123.5234	$123.52	$123.50	$123.50
Purchase #6	$82.52	12.851%	$93.1246	$93.12	$93.10	$93.10
Purchase #7	$196.40	7.516%	$211.1614	$211.16	$211.15	$211.20
7 purchase totals =	$1,015.83		$1,096.2442	$1,096.24	$1,096.20	$1,096.20