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	$142.70	9.552%	$156.3307	$156.33	$156.35	$156.30
Purchase #2	$36.31	10.693%	$40.1926	$40.19	$40.20	$40.20
Purchase #3	$156.66	10.401%	$172.9542	$172.95	$172.95	$173.00
Purchase #4	$134.90	4.102%	$140.4336	$140.43	$140.45	$140.40
Purchase #5	$6.79	4.695%	$7.1088	$7.11	$7.10	$7.10
Purchase #6	$20.90	5.301%	$22.0079	$22.01	$22.00	$22.00
Purchase #7	$184.89	7.170%	$198.1466	$198.15	$198.15	$198.10
7 purchase totals =	$683.15		$737.1744	$737.17	$737.20	$737.10