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	$150.25	11.866%	$168.0787	$168.08	$168.10	$168.10
Purchase #2	$41.51	6.794%	$44.3302	$44.33	$44.35	$44.30
Purchase #3	$98.45	4.696%	$103.0732	$103.07	$103.05	$103.10
Purchase #4	$229.46	12.291%	$257.6629	$257.66	$257.65	$257.70
Purchase #5	$234.78	4.210%	$244.6642	$244.66	$244.65	$244.70
Purchase #6	$165.72	12.432%	$186.3223	$186.32	$186.30	$186.30
Purchase #7	$82.46	8.563%	$89.521	$89.52	$89.50	$89.50
7 purchase totals =	$1,002.63		$1,093.6525	$1,093.64	$1,093.60	$1,093.70