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	$137.66	3.762%	$142.8388	$142.84	$142.85	$142.80
Purchase #2	$158.89	3.570%	$164.5624	$164.56	$164.55	$164.60
Purchase #3	$116.72	12.310%	$131.0882	$131.09	$131.10	$131.10
Purchase #4	$35.94	13.185%	$40.6787	$40.68	$40.70	$40.70
Purchase #5	$175.28	4.785%	$183.6671	$183.67	$183.65	$183.70
Purchase #6	$42.27	6.291%	$44.9292	$44.93	$44.95	$44.90
Purchase #7	$83.28	10.390%	$91.9328	$91.93	$91.95	$91.90
7 purchase totals =	$750.04		$799.6972	$799.70	$799.75	$799.70