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	$19.73	11.102%	$21.9204	$21.92	$21.90	$21.90
Purchase #2	$102.93	10.628%	$113.8694	$113.87	$113.85	$113.90
Purchase #3	$118.33	12.493%	$133.113	$133.11	$133.10	$133.10
Purchase #4	$159.56	12.807%	$179.9948	$179.99	$180.00	$180.00
Purchase #5	$105.62	5.591%	$111.5252	$111.53	$111.55	$111.50
Purchase #6	$240.31	8.418%	$260.5393	$260.54	$260.55	$260.50
Purchase #7	$117.92	11.362%	$131.3181	$131.32	$131.30	$131.30
7 purchase totals =	$864.40		$952.2802	$952.28	$952.25	$952.20