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	$97.53	5.106%	$102.5099	$102.51	$102.50	$102.50
Purchase #2	$44.79	6.646%	$47.7667	$47.77	$47.75	$47.80
Purchase #3	$77.60	4.296%	$80.9337	$80.93	$80.95	$80.90
Purchase #4	$77.91	6.340%	$82.8495	$82.85	$82.85	$82.80
Purchase #5	$162.82	13.780%	$185.2566	$185.26	$185.25	$185.30
Purchase #6	$127.63	7.174%	$136.7862	$136.79	$136.80	$136.80
Purchase #7	$51.92	3.844%	$53.9158	$53.92	$53.90	$53.90
7 purchase totals =	$640.20		$690.0184	$690.03	$690.00	$690.00