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	$94.59	6.602%	$100.8348	$100.83	$100.85	$100.80
Purchase #2	$58.45	7.439%	$62.7981	$62.80	$62.80	$62.80
Purchase #3	$55.47	11.779%	$62.0038	$62.00	$62.00	$62.00
Purchase #4	$136.76	5.310%	$144.022	$144.02	$144.00	$144.00
Purchase #5	$28.57	12.643%	$32.1821	$32.18	$32.20	$32.20
Purchase #6	$228.63	3.705%	$237.1007	$237.10	$237.10	$237.10
Purchase #7	$27.86	8.477%	$30.2217	$30.22	$30.20	$30.20
7 purchase totals =	$630.33		$669.1632	$669.15	$669.15	$669.10