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	$124.56	6.608%	$132.7909	$132.79	$132.80	$132.80
Purchase #2	$239.86	8.763%	$260.8789	$260.88	$260.90	$260.90
Purchase #3	$211.58	3.189%	$218.3273	$218.33	$218.35	$218.30
Purchase #4	$148.47	13.328%	$168.2581	$168.26	$168.25	$168.30
Purchase #5	$62.59	8.569%	$67.9533	$67.95	$67.95	$68.00
Purchase #6	$40.28	5.529%	$42.5071	$42.51	$42.50	$42.50
Purchase #7	$101.52	4.359%	$105.9453	$105.95	$105.95	$105.90
7 purchase totals =	$928.86		$996.6609	$996.67	$996.70	$996.70