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	$92.62	8.398%	$100.3982	$100.40	$100.40	$100.40
Purchase #2	$81.71	10.665%	$90.4244	$90.42	$90.40	$90.40
Purchase #3	$156.79	5.403%	$165.2614	$165.26	$165.25	$165.30
Purchase #4	$208.91	11.729%	$233.4131	$233.41	$233.40	$233.40
Purchase #5	$249.94	5.204%	$262.9469	$262.95	$262.95	$262.90
Purchase #6	$142.74	12.263%	$160.2442	$160.24	$160.25	$160.20
Purchase #7	$171.37	5.812%	$181.33	$181.33	$181.35	$181.30
7 purchase totals =	$1,104.08		$1,194.0182	$1,194.01	$1,194.00	$1,193.90