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	$208.33	11.837%	$232.99	$232.99	$233.00	$233.00
Purchase #2	$118.92	10.756%	$131.711	$131.71	$131.70	$131.70
Purchase #3	$33.55	12.509%	$37.7468	$37.75	$37.75	$37.70
Purchase #4	$47.76	12.730%	$53.8398	$53.84	$53.85	$53.80
Purchase #5	$136.46	4.360%	$142.4097	$142.41	$142.40	$142.40
Purchase #6	$27.31	9.165%	$29.813	$29.81	$29.80	$29.80
Purchase #7	$33.86	12.609%	$38.1294	$38.13	$38.15	$38.10
7 purchase totals =	$606.19		$666.6397	$666.64	$666.65	$666.50