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	$109.65	7.175%	$117.5174	$117.52	$117.50	$117.50
Purchase #2	$178.33	12.160%	$200.0149	$200.01	$200.00	$200.00
Purchase #3	$83.40	7.343%	$89.5241	$89.52	$89.50	$89.50
Purchase #4	$129.45	10.675%	$143.2688	$143.27	$143.25	$143.30
Purchase #5	$73.73	4.853%	$77.3081	$77.31	$77.30	$77.30
Purchase #6	$240.89	3.532%	$249.3982	$249.40	$249.40	$249.40
Purchase #7	$70.30	11.870%	$78.6446	$78.64	$78.65	$78.60
7 purchase totals =	$885.75		$955.6761	$955.67	$955.60	$955.60