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	$153.71	6.761%	$164.1023	$164.10	$164.10	$164.10
Purchase #2	$10.83	9.132%	$11.819	$11.82	$11.80	$11.80
Purchase #3	$243.25	5.450%	$256.5071	$256.51	$256.50	$256.50
Purchase #4	$148.76	13.211%	$168.4127	$168.41	$168.40	$168.40
Purchase #5	$115.61	13.401%	$131.1029	$131.10	$131.10	$131.10
Purchase #6	$84.73	9.754%	$92.9946	$92.99	$93.00	$93.00
Purchase #7	$14.89	12.664%	$16.7757	$16.78	$16.80	$16.80
7 purchase totals =	$771.78		$841.7143	$841.71	$841.70	$841.70