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	$70.38	11.718%	$78.6271	$78.63	$78.65	$78.60
Purchase #2	$117.83	8.429%	$127.7619	$127.76	$127.75	$127.80
Purchase #3	$163.96	12.534%	$184.5107	$184.51	$184.50	$184.50
Purchase #4	$245.39	11.757%	$274.2405	$274.24	$274.25	$274.20
Purchase #5	$14.55	9.444%	$15.9241	$15.92	$15.90	$15.90
Purchase #6	$171.98	8.331%	$186.3077	$186.31	$186.30	$186.30
Purchase #7	$187.64	12.255%	$210.6353	$210.64	$210.65	$210.60
7 purchase totals =	$971.73		$1,078.0073	$1,078.01	$1,078.00	$1,077.90