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	$157.28	4.838%	$164.8892	$164.89	$164.90	$164.90
Purchase #2	$55.57	12.444%	$62.4851	$62.49	$62.50	$62.50
Purchase #3	$39.34	10.299%	$43.3916	$43.39	$43.40	$43.40
Purchase #4	$118.79	4.242%	$123.8291	$123.83	$123.85	$123.80
Purchase #5	$25.30	8.627%	$27.4826	$27.48	$27.50	$27.50
Purchase #6	$220.59	5.504%	$232.7313	$232.73	$232.75	$232.70
Purchase #7	$118.50	8.395%	$128.4481	$128.45	$128.45	$128.40
7 purchase totals =	$735.37		$783.2570	$783.26	$783.35	$783.20