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	$38.27	5.637%	$40.4273	$40.43	$40.45	$40.40
Purchase #2	$62.40	12.825%	$70.4028	$70.40	$70.40	$70.40
Purchase #3	$107.84	3.282%	$111.3793	$111.38	$111.40	$111.40
Purchase #4	$172.75	13.471%	$196.0212	$196.02	$196.00	$196.00
Purchase #5	$106.51	5.806%	$112.694	$112.69	$112.70	$112.70
Purchase #6	$33.97	6.835%	$36.2918	$36.29	$36.30	$36.30
Purchase #7	$94.53	9.652%	$103.654	$103.65	$103.65	$103.70
7 purchase totals =	$616.27		$670.8704	$670.86	$670.90	$670.90