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	$170.50	10.175%	$187.8484	$187.85	$187.85	$187.80
Purchase #2	$186.45	7.601%	$200.6221	$200.62	$200.60	$200.60
Purchase #3	$224.50	11.183%	$249.6058	$249.61	$249.60	$249.60
Purchase #4	$66.83	6.368%	$71.0857	$71.09	$71.10	$71.10
Purchase #5	$97.56	7.471%	$104.8487	$104.85	$104.85	$104.80
Purchase #6	$55.77	12.342%	$62.6531	$62.65	$62.65	$62.70
Purchase #7	$63.30	12.333%	$71.1068	$71.11	$71.10	$71.10
7 purchase totals =	$864.91		$947.7706	$947.78	$947.75	$947.70