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	$65.55	13.412%	$74.3416	$74.34	$74.35	$74.30
Purchase #2	$109.57	12.597%	$123.3725	$123.37	$123.35	$123.40
Purchase #3	$30.73	4.655%	$32.1605	$32.16	$32.15	$32.20
Purchase #4	$222.99	8.235%	$241.3532	$241.35	$241.35	$241.40
Purchase #5	$20.56	11.369%	$22.8975	$22.90	$22.90	$22.90
Purchase #6	$116.58	6.787%	$124.4923	$124.49	$124.50	$124.50
Purchase #7	$74.51	10.208%	$82.116	$82.12	$82.10	$82.10
7 purchase totals =	$640.49		$700.7336	$700.73	$700.70	$700.80