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	$131.46	4.240%	$137.0339	$137.03	$137.05	$137.00
Purchase #2	$108.38	13.408%	$122.9116	$122.91	$122.90	$122.90
Purchase #3	$92.78	11.873%	$103.7958	$103.80	$103.80	$103.80
Purchase #4	$70.77	11.201%	$78.6969	$78.70	$78.70	$78.70
Purchase #5	$5.96	9.391%	$6.5197	$6.52	$6.50	$6.50
Purchase #6	$170.60	9.311%	$186.4846	$186.48	$186.50	$186.50
Purchase #7	$135.77	11.532%	$151.427	$151.43	$151.45	$151.40
7 purchase totals =	$715.72		$786.8695	$786.87	$786.90	$786.80