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	$126.28	12.417%	$141.9602	$141.96	$141.95	$142.00
Purchase #2	$210.70	4.756%	$220.7209	$220.72	$220.70	$220.70
Purchase #3	$108.31	13.821%	$123.2795	$123.28	$123.30	$123.30
Purchase #4	$154.56	11.259%	$171.9619	$171.96	$171.95	$172.00
Purchase #5	$58.65	5.704%	$61.9954	$62.00	$62.00	$62.00
Purchase #6	$60.32	9.353%	$65.9617	$65.96	$65.95	$66.00
Purchase #7	$107.56	12.392%	$120.8888	$120.89	$120.90	$120.90
7 purchase totals =	$826.38		$906.7684	$906.77	$906.75	$906.90