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	$144.54	13.814%	$164.5068	$164.51	$164.50	$164.50
Purchase #2	$212.63	12.150%	$238.4645	$238.46	$238.45	$238.50
Purchase #3	$46.61	12.819%	$52.5849	$52.58	$52.60	$52.60
Purchase #4	$88.28	6.628%	$94.1312	$94.13	$94.15	$94.10
Purchase #5	$8.30	5.526%	$8.7587	$8.76	$8.75	$8.80
Purchase #6	$208.66	10.192%	$229.9266	$229.93	$229.95	$229.90
Purchase #7	$40.83	5.860%	$43.2226	$43.22	$43.20	$43.20
7 purchase totals =	$749.85		$831.5953	$831.59	$831.60	$831.60