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	$78.58	12.157%	$88.133	$88.13	$88.15	$88.10
Purchase #2	$107.60	3.718%	$111.6006	$111.60	$111.60	$111.60
Purchase #3	$67.88	5.620%	$71.6949	$71.69	$71.70	$71.70
Purchase #4	$88.39	7.520%	$95.0369	$95.04	$95.05	$95.00
Purchase #5	$142.44	10.184%	$156.9461	$156.95	$156.95	$156.90
Purchase #6	$57.94	10.280%	$63.8962	$63.90	$63.90	$63.90
Purchase #7	$11.68	11.263%	$12.9955	$13.00	$13.00	$13.00
7 purchase totals =	$554.51		$600.3032	$600.31	$600.35	$600.20