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	$17.77	5.688%	$18.7808	$18.78	$18.80	$18.80
Purchase #2	$146.73	6.512%	$156.2851	$156.29	$156.30	$156.30
Purchase #3	$86.26	4.416%	$90.0692	$90.07	$90.05	$90.10
Purchase #4	$141.55	12.553%	$159.3188	$159.32	$159.30	$159.30
Purchase #5	$76.75	10.372%	$84.7105	$84.71	$84.70	$84.70
Purchase #6	$143.59	10.361%	$158.4674	$158.47	$158.45	$158.50
Purchase #7	$238.94	12.119%	$267.8971	$267.90	$267.90	$267.90
7 purchase totals =	$851.59		$935.5289	$935.54	$935.50	$935.60