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	$194.40	5.188%	$204.4855	$204.49	$204.50	$204.50
Purchase #2	$116.89	11.707%	$130.5743	$130.57	$130.55	$130.60
Purchase #3	$18.80	11.762%	$21.0113	$21.01	$21.00	$21.00
Purchase #4	$132.78	6.477%	$141.3802	$141.38	$141.40	$141.40
Purchase #5	$213.48	3.773%	$221.5346	$221.53	$221.55	$221.50
Purchase #6	$32.57	13.863%	$37.0852	$37.09	$37.10	$37.10
Purchase #7	$123.67	6.731%	$131.9942	$131.99	$132.00	$132.00
7 purchase totals =	$832.59		$888.0653	$888.06	$888.10	$888.10