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	$243.31	6.224%	$258.4536	$258.45	$258.45	$258.50
Purchase #2	$56.58	5.874%	$59.9035	$59.90	$59.90	$59.90
Purchase #3	$109.74	8.111%	$118.641	$118.64	$118.65	$118.60
Purchase #4	$195.72	5.564%	$206.6099	$206.61	$206.60	$206.60
Purchase #5	$75.59	3.296%	$78.0814	$78.08	$78.10	$78.10
Purchase #6	$178.28	4.595%	$186.472	$186.47	$186.45	$186.50
Purchase #7	$99.82	5.782%	$105.5916	$105.59	$105.60	$105.60
7 purchase totals =	$959.04		$1,013.7530	$1,013.74	$1,013.75	$1,013.80