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	$31.71	7.678%	$34.1447	$34.14	$34.15	$34.10
Purchase #2	$67.31	13.274%	$76.2447	$76.24	$76.25	$76.20
Purchase #3	$103.51	9.151%	$112.9822	$112.98	$113.00	$113.00
Purchase #4	$98.30	13.469%	$111.54	$111.54	$111.55	$111.50
Purchase #5	$83.50	9.491%	$91.425	$91.43	$91.45	$91.40
Purchase #6	$25.69	5.735%	$27.1633	$27.16	$27.15	$27.20
Purchase #7	$92.41	12.810%	$104.2477	$104.25	$104.25	$104.20
7 purchase totals =	$502.43		$557.7476	$557.74	$557.80	$557.60