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	$11.75	12.550%	$13.2246	$13.22	$13.20	$13.20
Purchase #2	$128.59	12.678%	$144.8926	$144.89	$144.90	$144.90
Purchase #3	$105.51	3.554%	$109.2598	$109.26	$109.25	$109.30
Purchase #4	$22.44	4.252%	$23.3941	$23.39	$23.40	$23.40
Purchase #5	$192.86	9.693%	$211.5539	$211.55	$211.55	$211.60
Purchase #6	$71.76	9.646%	$78.682	$78.68	$78.70	$78.70
Purchase #7	$43.82	7.306%	$47.0215	$47.02	$47.00	$47.00
7 purchase totals =	$576.73		$628.0285	$628.01	$628.00	$628.10