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	$203.95	9.770%	$223.8759	$223.88	$223.90	$223.90
Purchase #2	$150.52	3.830%	$156.2849	$156.28	$156.30	$156.30
Purchase #3	$57.35	6.526%	$61.0927	$61.09	$61.10	$61.10
Purchase #4	$72.69	6.546%	$77.4483	$77.45	$77.45	$77.40
Purchase #5	$160.47	11.350%	$178.6833	$178.68	$178.70	$178.70
Purchase #6	$49.83	5.686%	$52.6633	$52.66	$52.65	$52.70
Purchase #7	$97.55	3.369%	$100.8365	$100.84	$100.85	$100.80
7 purchase totals =	$792.36		$850.8849	$850.88	$850.95	$850.90