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	$242.38	11.773%	$270.9154	$270.92	$270.90	$270.90
Purchase #2	$52.63	12.484%	$59.2003	$59.20	$59.20	$59.20
Purchase #3	$220.46	9.868%	$242.215	$242.22	$242.20	$242.20
Purchase #4	$146.92	7.252%	$157.5746	$157.57	$157.55	$157.60
Purchase #5	$149.93	10.618%	$165.8496	$165.85	$165.85	$165.80
Purchase #6	$203.89	8.136%	$220.4785	$220.48	$220.50	$220.50
Purchase #7	$50.86	3.200%	$52.4875	$52.49	$52.50	$52.50
7 purchase totals =	$1,067.07		$1,168.7209	$1,168.73	$1,168.70	$1,168.70