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	$248.32	12.599%	$279.6058	$279.61	$279.60	$279.60
Purchase #2	$15.87	12.457%	$17.8469	$17.85	$17.85	$17.80
Purchase #3	$245.54	5.167%	$258.2271	$258.23	$258.25	$258.20
Purchase #4	$148.89	11.113%	$165.4361	$165.44	$165.45	$165.40
Purchase #5	$128.98	6.867%	$137.8371	$137.84	$137.85	$137.80
Purchase #6	$5.54	5.440%	$5.8414	$5.84	$5.85	$5.80
Purchase #7	$171.41	5.523%	$180.877	$180.88	$180.90	$180.90
7 purchase totals =	$964.55		$1,045.6714	$1,045.69	$1,045.75	$1,045.50