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	$30.32	8.460%	$32.8851	$32.89	$32.90	$32.90
Purchase #2	$67.62	7.783%	$72.8829	$72.88	$72.90	$72.90
Purchase #3	$205.77	13.451%	$233.4481	$233.45	$233.45	$233.40
Purchase #4	$213.95	4.570%	$223.7275	$223.73	$223.75	$223.70
Purchase #5	$211.73	11.772%	$236.6549	$236.65	$236.65	$236.70
Purchase #6	$11.29	13.656%	$12.8318	$12.83	$12.85	$12.80
Purchase #7	$47.82	7.248%	$51.286	$51.29	$51.30	$51.30
7 purchase totals =	$788.50		$863.7163	$863.72	$863.80	$863.70