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	$51.31	3.172%	$52.9376	$52.94	$52.95	$52.90
Purchase #2	$136.33	10.318%	$150.3965	$150.40	$150.40	$150.40
Purchase #3	$35.55	4.190%	$37.0395	$37.04	$37.05	$37.00
Purchase #4	$183.72	7.525%	$197.5449	$197.54	$197.55	$197.50
Purchase #5	$212.36	8.539%	$230.4934	$230.49	$230.50	$230.50
Purchase #6	$41.89	6.218%	$44.4947	$44.49	$44.50	$44.50
Purchase #7	$62.52	7.855%	$67.4309	$67.43	$67.45	$67.40
7 purchase totals =	$723.68		$780.3375	$780.33	$780.40	$780.20