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	$146.60	12.585%	$165.0496	$165.05	$165.05	$165.00
Purchase #2	$166.89	11.149%	$185.4966	$185.50	$185.50	$185.50
Purchase #3	$62.51	10.571%	$69.1179	$69.12	$69.10	$69.10
Purchase #4	$213.65	9.782%	$234.5492	$234.55	$234.55	$234.50
Purchase #5	$150.95	10.712%	$167.1198	$167.12	$167.10	$167.10
Purchase #6	$218.41	9.276%	$238.6697	$238.67	$238.65	$238.70
Purchase #7	$68.25	6.249%	$72.5149	$72.51	$72.50	$72.50
7 purchase totals =	$1,027.26		$1,132.5177	$1,132.52	$1,132.45	$1,132.40