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	$126.69	12.189%	$142.1322	$142.13	$142.15	$142.10
Purchase #2	$68.58	3.268%	$70.8212	$70.82	$70.80	$70.80
Purchase #3	$194.88	7.254%	$209.0166	$209.02	$209.00	$209.00
Purchase #4	$170.83	12.485%	$192.1581	$192.16	$192.15	$192.20
Purchase #5	$143.39	3.819%	$148.8661	$148.87	$148.85	$148.90
Purchase #6	$75.84	3.347%	$78.3784	$78.38	$78.40	$78.40
Purchase #7	$19.87	11.539%	$22.1628	$22.16	$22.15	$22.20
7 purchase totals =	$800.08		$863.5354	$863.54	$863.50	$863.60