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	$173.87	3.709%	$180.3188	$180.32	$180.30	$180.30
Purchase #2	$217.50	13.484%	$246.8277	$246.83	$246.85	$246.80
Purchase #3	$28.36	13.358%	$32.1483	$32.15	$32.15	$32.10
Purchase #4	$122.27	4.807%	$128.1475	$128.15	$128.15	$128.10
Purchase #5	$60.80	12.162%	$68.1945	$68.19	$68.20	$68.20
Purchase #6	$28.34	12.531%	$31.8913	$31.89	$31.90	$31.90
Purchase #7	$38.74	8.847%	$42.1673	$42.17	$42.15	$42.20
7 purchase totals =	$669.88		$729.6954	$729.70	$729.70	$729.60