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	$229.40	9.126%	$250.335	$250.34	$250.35	$250.30
Purchase #2	$145.94	4.381%	$152.3336	$152.33	$152.35	$152.30
Purchase #3	$217.63	10.509%	$240.5007	$240.50	$240.50	$240.50
Purchase #4	$14.48	11.169%	$16.0973	$16.10	$16.10	$16.10
Purchase #5	$188.66	6.321%	$200.5852	$200.59	$200.60	$200.60
Purchase #6	$85.38	3.389%	$88.2735	$88.27	$88.25	$88.30
Purchase #7	$245.96	8.587%	$267.0806	$267.08	$267.10	$267.10
7 purchase totals =	$1,127.45		$1,215.2059	$1,215.21	$1,215.25	$1,215.20