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	$170.59	10.147%	$187.8998	$187.90	$187.90	$187.90
Purchase #2	$53.45	4.150%	$55.6682	$55.67	$55.65	$55.70
Purchase #3	$151.61	8.573%	$164.6075	$164.61	$164.60	$164.60
Purchase #4	$179.59	11.650%	$200.5122	$200.51	$200.50	$200.50
Purchase #5	$6.86	3.184%	$7.0784	$7.08	$7.10	$7.10
Purchase #6	$38.51	5.518%	$40.635	$40.64	$40.65	$40.60
Purchase #7	$79.31	11.203%	$88.1951	$88.20	$88.20	$88.20
7 purchase totals =	$679.92		$744.5962	$744.61	$744.60	$744.60