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	$123.52	11.588%	$137.8335	$137.83	$137.85	$137.80
Purchase #2	$29.77	7.249%	$31.928	$31.93	$31.95	$31.90
Purchase #3	$91.62	11.503%	$102.159	$102.16	$102.15	$102.20
Purchase #4	$31.49	5.417%	$33.1958	$33.20	$33.20	$33.20
Purchase #5	$128.33	3.698%	$133.0756	$133.08	$133.10	$133.10
Purchase #6	$135.68	5.251%	$142.8046	$142.80	$142.80	$142.80
Purchase #7	$196.54	9.823%	$215.8461	$215.85	$215.85	$215.80
7 purchase totals =	$736.95		$796.8426	$796.85	$796.90	$796.80