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	$27.57	10.230%	$30.3904	$30.39	$30.40	$30.40
Purchase #2	$58.58	4.648%	$61.3028	$61.30	$61.30	$61.30
Purchase #3	$192.43	11.800%	$215.1367	$215.14	$215.15	$215.10
Purchase #4	$113.54	12.272%	$127.4736	$127.47	$127.45	$127.50
Purchase #5	$37.53	10.286%	$41.3903	$41.39	$41.40	$41.40
Purchase #6	$196.69	11.159%	$218.6386	$218.64	$218.65	$218.60
Purchase #7	$55.66	10.632%	$61.5778	$61.58	$61.60	$61.60
7 purchase totals =	$682.00		$755.9102	$755.91	$755.95	$755.90