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	$68.80	3.761%	$71.3876	$71.39	$71.40	$71.40
Purchase #2	$62.93	7.523%	$67.6642	$67.66	$67.65	$67.70
Purchase #3	$16.49	9.838%	$18.1123	$18.11	$18.10	$18.10
Purchase #4	$111.87	11.573%	$124.8167	$124.82	$124.80	$124.80
Purchase #5	$31.50	11.524%	$35.1301	$35.13	$35.15	$35.10
Purchase #6	$106.43	10.712%	$117.8308	$117.83	$117.85	$117.80
Purchase #7	$176.53	4.847%	$185.0864	$185.09	$185.10	$185.10
7 purchase totals =	$574.55		$620.0281	$620.03	$620.05	$620.00