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	$113.27	9.811%	$124.3829	$124.38	$124.40	$124.40
Purchase #2	$174.59	12.792%	$196.9236	$196.92	$196.90	$196.90
Purchase #3	$183.36	3.795%	$190.3185	$190.32	$190.30	$190.30
Purchase #4	$186.35	4.643%	$195.0022	$195.00	$195.00	$195.00
Purchase #5	$90.73	10.656%	$100.3982	$100.40	$100.40	$100.40
Purchase #6	$118.58	11.416%	$132.1171	$132.12	$132.10	$132.10
Purchase #7	$46.48	7.569%	$49.9981	$50.00	$50.00	$50.00
7 purchase totals =	$913.36		$989.1406	$989.14	$989.10	$989.10