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	$234.77	8.747%	$255.3053	$255.31	$255.30	$255.30
Purchase #2	$24.87	12.646%	$28.0151	$28.02	$28.00	$28.00
Purchase #3	$197.52	6.240%	$209.8452	$209.85	$209.85	$209.80
Purchase #4	$248.55	8.780%	$270.3727	$270.37	$270.35	$270.40
Purchase #5	$20.72	3.445%	$21.4338	$21.43	$21.45	$21.40
Purchase #6	$42.34	8.114%	$45.7755	$45.78	$45.80	$45.80
Purchase #7	$105.27	7.519%	$113.1853	$113.19	$113.20	$113.20
7 purchase totals =	$874.04		$943.9329	$943.95	$943.95	$943.90