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	$140.85	10.848%	$156.1294	$156.13	$156.15	$156.10
Purchase #2	$132.75	5.370%	$139.8787	$139.88	$139.90	$139.90
Purchase #3	$207.81	3.635%	$215.3639	$215.36	$215.35	$215.40
Purchase #4	$250.76	10.700%	$277.5913	$277.59	$277.60	$277.60
Purchase #5	$39.47	7.436%	$42.405	$42.41	$42.40	$42.40
Purchase #6	$248.43	11.559%	$277.146	$277.15	$277.15	$277.10
Purchase #7	$103.91	8.312%	$112.547	$112.55	$112.55	$112.50
7 purchase totals =	$1,123.98		$1,221.0613	$1,221.07	$1,221.10	$1,221.00