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	$49.32	3.559%	$51.0753	$51.08	$51.10	$51.10
Purchase #2	$137.47	10.423%	$151.7985	$151.80	$151.80	$151.80
Purchase #3	$49.63	12.499%	$55.8333	$55.83	$55.85	$55.80
Purchase #4	$30.59	7.568%	$32.9051	$32.91	$32.90	$32.90
Purchase #5	$128.83	4.518%	$134.6505	$134.65	$134.65	$134.70
Purchase #6	$160.81	4.429%	$167.9323	$167.93	$167.95	$167.90
Purchase #7	$113.36	13.178%	$128.2986	$128.30	$128.30	$128.30
7 purchase totals =	$670.01		$722.4936	$722.50	$722.55	$722.50