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	$156.58	5.625%	$165.3876	$165.39	$165.40	$165.40
Purchase #2	$107.61	4.523%	$112.4772	$112.48	$112.50	$112.50
Purchase #3	$210.74	12.381%	$236.8317	$236.83	$236.85	$236.80
Purchase #4	$174.38	3.137%	$179.8503	$179.85	$179.85	$179.90
Purchase #5	$118.43	10.170%	$130.4743	$130.47	$130.45	$130.50
Purchase #6	$64.94	8.416%	$70.4054	$70.41	$70.40	$70.40
Purchase #7	$82.53	8.347%	$89.4188	$89.42	$89.40	$89.40
7 purchase totals =	$915.21		$984.8453	$984.85	$984.85	$984.90