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	$178.48	4.152%	$185.8905	$185.89	$185.90	$185.90
Purchase #2	$141.61	10.304%	$156.2015	$156.20	$156.20	$156.20
Purchase #3	$196.71	3.243%	$203.0893	$203.09	$203.10	$203.10
Purchase #4	$136.87	13.274%	$155.0381	$155.04	$155.05	$155.00
Purchase #5	$222.82	10.557%	$246.3431	$246.34	$246.35	$246.30
Purchase #6	$85.35	11.540%	$95.1994	$95.20	$95.20	$95.20
Purchase #7	$40.52	3.500%	$41.9382	$41.94	$41.95	$41.90
7 purchase totals =	$1,002.36		$1,083.7001	$1,083.70	$1,083.75	$1,083.60