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	$187.79	6.807%	$200.5729	$200.57	$200.55	$200.60
Purchase #2	$208.32	12.135%	$233.5996	$233.60	$233.60	$233.60
Purchase #3	$201.44	5.461%	$212.4406	$212.44	$212.45	$212.40
Purchase #4	$185.59	13.108%	$209.9171	$209.92	$209.90	$209.90
Purchase #5	$136.78	10.751%	$151.4852	$151.49	$151.50	$151.50
Purchase #6	$244.67	5.175%	$257.3317	$257.33	$257.35	$257.30
Purchase #7	$13.95	11.188%	$15.5107	$15.51	$15.50	$15.50
7 purchase totals =	$1,178.54		$1,280.8578	$1,280.86	$1,280.85	$1,280.80