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	$71.67	9.175%	$78.2457	$78.25	$78.25	$78.20
Purchase #2	$24.68	11.237%	$27.4533	$27.45	$27.45	$27.50
Purchase #3	$88.96	8.868%	$96.849	$96.85	$96.85	$96.80
Purchase #4	$229.69	5.742%	$242.8788	$242.88	$242.90	$242.90
Purchase #5	$219.52	5.286%	$231.1238	$231.12	$231.10	$231.10
Purchase #6	$55.51	6.532%	$59.1359	$59.14	$59.15	$59.10
Purchase #7	$127.52	5.646%	$134.7198	$134.72	$134.70	$134.70
7 purchase totals =	$817.55		$870.4063	$870.41	$870.40	$870.30