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	$106.91	3.280%	$110.4166	$110.42	$110.40	$110.40
Purchase #2	$81.40	9.729%	$89.3194	$89.32	$89.30	$89.30
Purchase #3	$118.74	6.106%	$125.9903	$125.99	$126.00	$126.00
Purchase #4	$103.42	7.685%	$111.3678	$111.37	$111.35	$111.40
Purchase #5	$16.75	8.357%	$18.1498	$18.15	$18.15	$18.10
Purchase #6	$72.72	7.425%	$78.1195	$78.12	$78.10	$78.10
Purchase #7	$86.44	11.759%	$96.6045	$96.60	$96.60	$96.60
7 purchase totals =	$586.38		$629.9679	$629.97	$629.90	$629.90