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	$68.74	3.341%	$71.0366	$71.04	$71.05	$71.00
Purchase #2	$137.61	3.759%	$142.7828	$142.78	$142.80	$142.80
Purchase #3	$97.98	4.708%	$102.5929	$102.59	$102.60	$102.60
Purchase #4	$174.86	12.610%	$196.9098	$196.91	$196.90	$196.90
Purchase #5	$122.66	7.441%	$131.7871	$131.79	$131.80	$131.80
Purchase #6	$11.67	5.775%	$12.3439	$12.34	$12.35	$12.30
Purchase #7	$162.28	5.337%	$170.9409	$170.94	$170.95	$170.90
7 purchase totals =	$775.80		$828.3940	$828.39	$828.45	$828.30