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	$36.85	5.380%	$38.8325	$38.83	$38.85	$38.80
Purchase #2	$52.71	5.114%	$55.4056	$55.41	$55.40	$55.40
Purchase #3	$62.67	6.323%	$66.6326	$66.63	$66.65	$66.60
Purchase #4	$230.42	10.769%	$255.2339	$255.23	$255.25	$255.20
Purchase #5	$62.26	7.703%	$67.0559	$67.06	$67.05	$67.10
Purchase #6	$87.61	10.673%	$96.9606	$96.96	$96.95	$97.00
Purchase #7	$123.80	7.341%	$132.8882	$132.89	$132.90	$132.90
7 purchase totals =	$656.32		$713.0093	$713.01	$713.05	$713.00