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	$51.83	10.390%	$57.2151	$57.22	$57.20	$57.20
Purchase #2	$150.25	6.544%	$160.0824	$160.08	$160.10	$160.10
Purchase #3	$111.41	12.749%	$125.6137	$125.61	$125.60	$125.60
Purchase #4	$114.73	3.434%	$118.6698	$118.67	$118.65	$118.70
Purchase #5	$52.69	13.530%	$59.819	$59.82	$59.80	$59.80
Purchase #6	$88.95	5.444%	$93.7924	$93.79	$93.80	$93.80
Purchase #7	$182.73	7.615%	$196.6449	$196.64	$196.65	$196.60
7 purchase totals =	$752.59		$811.8373	$811.83	$811.80	$811.80